text: """
  Useful functions.  If non-original, see function for citation.
  
  
  
  """
  from __future__ import print_function
  
  #-----------------------------------------------------------------------------
  # Copyright (c) 2013, yt Development Team.
  #
  # Distributed under the terms of the Modified BSD License.
  #
  # The full license is in the file COPYING.txt, distributed with this software.
  #-----------------------------------------------------------------------------
  
  import errno
  from yt.extern.six import string_types
  from yt.extern.six.moves import input, builtins
  import time
  import inspect
  import traceback
  import sys
  import pdb
  import os
  import re
  import contextlib
  import warnings
  import struct
  import subprocess
  import numpy as np
  import itertools
  import base64
  import numpy
  import matplotlib
  import getpass
  from math import floor, ceil
  from numbers import Number as numeric_type
  
  from yt.extern.six.moves import urllib
  from yt.utilities.logger import ytLogger as mylog
  from yt.utilities.lru_cache import lru_cache
  from yt.utilities.exceptions import \
      YTInvalidWidthError, \
      YTEquivalentDimsError
  from yt.extern.tqdm import tqdm
  from yt.units.yt_array import YTArray, YTQuantity
  from functools import wraps
  
  # Some functions for handling sequences and other types
  
  def iterable(obj):
      """
      Grabbed from Python Cookbook / matplotlib.cbook.  Returns true/false for
      *obj* iterable.
      """
      try: len(obj)
      except: return False
      return True
  
  def ensure_list(obj):
      """
      This function ensures that *obj* is a list.  Typically used to convert a
      string to a list, for instance ensuring the *fields* as an argument is a
      list.
      """
      if obj is None:
          return [obj]
      if not isinstance(obj, list):
          return [obj]
      return obj
  
  def ensure_numpy_array(obj):
      """
      This function ensures that *obj* is a numpy array. Typically used to
      convert scalar, list or tuple argument passed to functions using Cython.
      """
      if isinstance(obj, np.ndarray):
          if obj.shape == ():
              return np.array([obj])
          # We cast to ndarray to catch ndarray subclasses
          return np.array(obj)
      elif isinstance(obj, (list, tuple)):
          return np.asarray(obj)
      else:
          return np.asarray([obj])
  
  def ensure_tuple(obj):
      """
      This function ensures that *obj* is a tuple.  Typically used to convert
      scalar, list, or array arguments specified by a user in a context where
      we assume a tuple internally
      """
      if isinstance(obj, tuple):
          return obj
      elif isinstance(obj, (list, np.ndarray)):
          return tuple(obj)
      else:
          return (obj,)
  
  def read_struct(f, fmt):
      """
      This reads a struct, and only that struct, from an open file.
      """
      s = f.read(struct.calcsize(fmt))
      return struct.unpack(fmt, s)
  
  def just_one(obj):
      # If we have an iterable, sometimes we only want one item
      if hasattr(obj,'flat'):
          if isinstance(obj, YTArray):
              return YTQuantity(obj.flat[0], obj.units, registry=obj.units.registry)
          return obj.flat[0]
      elif iterable(obj):
          return obj[0]
      return obj
  
  
  def compare_dicts(dict1, dict2):
      if not set(dict1) <= set(dict2):
          return False
      for key in dict1.keys():
          if dict1[key] is not None and dict2[key] is not None:
              if isinstance(dict1[key], dict):
                  if compare_dicts(dict1[key], dict2[key]):
                      continue
                  else:
                      return False
              try:
                  comparison = (dict1[key] == dict2[key]).all()
              except AttributeError:
                  comparison = (dict1[key] == dict2[key])
              if not comparison:
                  return False
      return True
  
  # Taken from
  # http://www.goldb.org/goldblog/2008/02/06/PythonConvertSecsIntoHumanReadableTimeStringHHMMSS.aspx
  def humanize_time(secs):
      """
      Takes *secs* and returns a nicely formatted string
      """
      mins, secs = divmod(secs, 60)
      hours, mins = divmod(mins, 60)
      return '%02d:%02d:%02d' % (hours, mins, secs)
  
  #
  # Some function wrappers that come in handy once in a while
  #
  
  # we use the resource module to get the memory page size
  
  try:
      import resource
  except ImportError:
      pass
  
  def get_memory_usage(subtract_share = False):
      """
      Returning resident size in megabytes
      """
      pid = os.getpid()
      try:
          pagesize = resource.getpagesize()
      except NameError:
          return -1024
      status_file = "/proc/%s/statm" % (pid)
      if not os.path.isfile(status_file):
          return -1024
      line = open(status_file).read()
      size, resident, share, text, library, data, dt = [int(i) for i in line.split()]
      if subtract_share: resident -= share
      return resident * pagesize / (1024 * 1024) # return in megs
  
  def time_execution(func):
      r"""
      Decorator for seeing how long a given function takes, depending on whether
      or not the global 'yt.timefunctions' config parameter is set.
      """
      @wraps(func)
      def wrapper(*arg, **kw):
          t1 = time.time()
          res = func(*arg, **kw)
          t2 = time.time()
          mylog.debug('%s took %0.3f s', func.__name__, (t2-t1))
          return res
      from yt.config import ytcfg
      if ytcfg.getboolean("yt","timefunctions") is True:
          return wrapper
      else:
          return func
  
  def print_tb(func):
      """
      This function is used as a decorate on a function to have the calling stack
      printed whenever that function is entered.
  
      This can be used like so:
  
      .. code-block:: python
  
         @print_tb
         def some_deeply_nested_function(...):
  
      """
      @wraps(func)
      def run_func(*args, **kwargs):
          traceback.print_stack()
          return func(*args, **kwargs)
      return run_func
  
  def rootonly(func):
      """
      This is a decorator that, when used, will only call the function on the
      root processor and then broadcast the results of the function to all other
      processors.
  
      This can be used like so:
  
      .. code-block:: python
  
         @rootonly
         def some_root_only_function(...):
  
      """
      from yt.config import ytcfg
      @wraps(func)
      def check_parallel_rank(*args, **kwargs):
          if ytcfg.getint("yt","__topcomm_parallel_rank") > 0:
              return
          return func(*args, **kwargs)
      return check_parallel_rank
  
  def rootloginfo(*args):
      from yt.config import ytcfg
      if ytcfg.getint("yt", "__topcomm_parallel_rank") > 0: return
      mylog.info(*args)
  
  def deprecate(replacement):
      def real_deprecate(func):
          """
          This decorator issues a deprecation warning.
  
          This can be used like so:
  
          .. code-block:: python
  
          @deprecate("new_function")
          def some_really_old_function(...):
  
          """
          @wraps(func)
          def run_func(*args, **kwargs):
              message = "%s has been deprecated and may be removed without notice!"
              if replacement is not None:
                  message += " Use %s instead." % replacement
              warnings.warn(message % func.__name__, DeprecationWarning,
                            stacklevel=2)
              func(*args, **kwargs)
          return run_func
      return real_deprecate
  
  def pdb_run(func):
      """
      This decorator inserts a pdb session on top of the call-stack into a
      function.
  
      This can be used like so:
  
      .. code-block:: python
  
         @pdb_run
         def some_function_to_debug(...):
  
      """
      @wraps(func)
      def wrapper(*args, **kw):
          pdb.runcall(func, *args, **kw)
      return wrapper
  
  __header = """
  == Welcome to the embedded IPython Shell ==
  
     You are currently inside the function:
       %(fname)s
  
     Defined in:
       %(filename)s:%(lineno)s
  """
  
  def insert_ipython(num_up=1):
      """
      Placed inside a function, this will insert an IPython interpreter at that
      current location.  This will enabled detailed inspection of the current
      execution environment, as well as (optional) modification of that environment.
      *num_up* refers to how many frames of the stack get stripped off, and
      defaults to 1 so that this function itself is stripped off.
      """
      import IPython
      from IPython.terminal.embed import InteractiveShellEmbed
      try:
          from traitlets.config.loader import Config
      except ImportError:
          from IPython.config.loader import Config
  
      frame = inspect.stack()[num_up]
      loc = frame[0].f_locals.copy()
      glo = frame[0].f_globals
      dd = dict(fname = frame[3], filename = frame[1],
                lineno = frame[2])
      cfg = Config()
      cfg.InteractiveShellEmbed.local_ns = loc
      cfg.InteractiveShellEmbed.global_ns = glo
      IPython.embed(config=cfg, banner2 = __header % dd)
      ipshell = InteractiveShellEmbed(config=cfg)
  
      del ipshell
  
  
  #
  # Our progress bar types and how to get one
  #
  
  class TqdmProgressBar(object):
      # This is a drop in replacement for pbar
      # called tqdm
      def __init__(self,title, maxval):
          self._pbar = tqdm(leave=True, total=maxval, desc=title)
          self.i = 0
      def update(self, i=None):
          if i is None:
              i = self.i + 1
          n = i - self.i
          self.i = i
          self._pbar.update(n)
      def finish(self):
          self._pbar.close()
  
  class DummyProgressBar(object):
      # This progressbar gets handed if we don't
      # want ANY output
      def __init__(self, *args, **kwargs):
          return
      def update(self, *args, **kwargs):
          return
      def finish(self, *args, **kwargs):
          return
  
  class ParallelProgressBar(object):
      # This is just a simple progress bar
      # that prints on start/stop
      def __init__(self, title, maxval):
          self.title = title
          mylog.info("Starting '%s'", title)
      def update(self, *args, **kwargs):
          return
      def finish(self):
          mylog.info("Finishing '%s'", self.title)
  
  class GUIProgressBar(object):
      def __init__(self, title, maxval):
          import wx
          self.maxval = maxval
          self.last = 0
          self._pbar = wx.ProgressDialog("Working...",
                      title, maximum=maxval,
                      style=wx.PD_REMAINING_TIME|wx.PD_ELAPSED_TIME|wx.PD_APP_MODAL)
      def update(self, val):
          # An update is only meaningful if it's on the order of 1/100 or greater
          if ceil(100*self.last / self.maxval) + 1 == \
             floor(100*val / self.maxval) or val == self.maxval:
              self._pbar.Update(val)
              self.last = val
      def finish(self):
          self._pbar.Destroy()
  
  def get_pbar(title, maxval, parallel=False):
      """
      This returns a progressbar of the most appropriate type, given a *title*
      and a *maxval*.
      """
      maxval = max(maxval, 1)
      from yt.config import ytcfg
      if ytcfg.getboolean("yt", "suppressStreamLogging") or \
         ytcfg.getboolean("yt", "__withintesting") or \
         maxval == 1: \
          return DummyProgressBar()
      elif ytcfg.getboolean("yt", "__parallel"):
          # If parallel is True, update progress on root only.
          if parallel:
              if is_root():
                  return TqdmProgressBar(title, maxval)
              else:
                  return DummyProgressBar()
          else:
              return ParallelProgressBar(title, maxval)
      pbar = TqdmProgressBar(title,maxval)
      return pbar
  
  def only_on_root(func, *args, **kwargs):
      """
      This function accepts a *func*, a set of *args* and *kwargs* and then only
      on the root processor calls the function.  All other processors get "None"
      handed back.
      """
      from yt.config import ytcfg
      if kwargs.pop("global_rootonly", False):
          cfg_option = "__global_parallel_rank"
      else:
          cfg_option = "__topcomm_parallel_rank"
      if not ytcfg.getboolean("yt","__parallel"):
          return func(*args,**kwargs)
      if ytcfg.getint("yt", cfg_option) > 0: return
      return func(*args, **kwargs)
  
  def is_root():
      """
      This function returns True if it is on the root processor of the
      topcomm and False otherwise.
      """
      from yt.config import ytcfg
      cfg_option = "__topcomm_parallel_rank"
      if not ytcfg.getboolean("yt","__parallel"):
          return True
      if ytcfg.getint("yt", cfg_option) > 0:
          return False
      return True
  
  
  #
  # Our signal and traceback handling functions
  #
  
  def signal_print_traceback(signo, frame):
      print(traceback.print_stack(frame))
  
  def signal_problem(signo, frame):
      raise RuntimeError()
  
  def signal_ipython(signo, frame):
      insert_ipython(2)
  
  def paste_traceback(exc_type, exc, tb):
      """
      This is a traceback handler that knows how to paste to the pastebin.
      Should only be used in sys.excepthook.
      """
      sys.__excepthook__(exc_type, exc, tb)
      from yt.extern.six.moves import StringIO, xmlrpc_client
      p = xmlrpc_client.ServerProxy(
              "http://paste.yt-project.org/xmlrpc/",
              allow_none=True)
      s = StringIO()
      traceback.print_exception(exc_type, exc, tb, file=s)
      s = s.getvalue()
      ret = p.pastes.newPaste('pytb', s, None, '', '', True)
      print()
      print("Traceback pasted to http://paste.yt-project.org/show/%s" % (ret))
      print()
  
  def paste_traceback_detailed(exc_type, exc, tb):
      """
      This is a traceback handler that knows how to paste to the pastebin.
      Should only be used in sys.excepthook.
      """
      import cgitb
      from yt.extern.six.moves import StringIO, xmlrpc_client
      s = StringIO()
      handler = cgitb.Hook(format="text", file = s)
      handler(exc_type, exc, tb)
      s = s.getvalue()
      print(s)
      p = xmlrpc_client.ServerProxy(
              "http://paste.yt-project.org/xmlrpc/",
              allow_none=True)
      ret = p.pastes.newPaste('text', s, None, '', '', True)
      print()
      print("Traceback pasted to http://paste.yt-project.org/show/%s" % (ret))
      print()
  
  _ss = "fURbBUUBE0cLXgETJnZgJRMXVhVGUQpQAUBuehQMUhJWRFFRAV1ERAtBXw1dAxMLXT4zXBFfABNN\nC0ZEXw1YUURHCxMXVlFERwxWCQw=\n"
  def _rdbeta(key):
      enc_s = base64.decodestring(_ss)
      dec_s = ''.join([ chr(ord(a) ^ ord(b)) for a, b in zip(enc_s, itertools.cycle(key)) ])
      print(dec_s)
  
  #
  # Some exceptions
  #
  
  class NoCUDAException(Exception):
      pass
  
  class YTEmptyClass(object):
      pass
  
  def update_hg_or_git(path):
      if os.path.exists(os.sep.join([path, '.hg'])):
          update_hg(path)
      elif os.path.exists(os.sep.join([path, '.git'])):
          update_git(path)
  
  def update_git(path):
      try:
          import git
      except ImportError:
          print("Updating and precise version information requires ")
          print("gitpython to be installed.")
          print("Try: pip install gitpython")
          return -1
      with open(os.path.join(path, "yt_updater.log"), "a") as f:
          repo = git.Repo(path)
          if repo.is_dirty(untracked_files=True):
              print("Changes have been made to the yt source code so I won't ")
              print("update the code. You will have to do this yourself.")
              print("Here's a set of sample commands:")
              print("")
              print("    $ cd %s" % (path))
              print("    $ git stash")
              print("    $ git checkout master")
              print("    $ git pull")
              print("    $ git stash pop")
              print("    $ %s setup.py develop" % (sys.executable))
              print("")
              return 1
          if repo.active_branch.name != 'master':
              print("yt repository is not tracking the master branch so I won't ")
              print("update the code. You will have to do this yourself.")
              print("Here's a set of sample commands:")
              print("")
              print("    $ cd %s" % (path))
              print("    $ git checkout master")
              print("    $ git pull")
              print("    $ %s setup.py develop" % (sys.executable))
              print("")
              return 1
          print("Updating the repository")
          f.write("Updating the repository\n\n")
          old_version = repo.git.rev_parse('HEAD', short=12)
          try:
              remote = repo.remotes.yt_upstream
          except AttributeError:
              remote = repo.create_remote(
                  'yt_upstream', url='https://github.com/yt-project/yt')
              remote.fetch()
          master = repo.heads.master
          master.set_tracking_branch(remote.refs.master)
          master.checkout()
          remote.pull()
          new_version = repo.git.rev_parse('HEAD', short=12)
          f.write('Updated from %s to %s\n\n' % (old_version, new_version))
          rebuild_modules(path, f)
      print('Updated successfully')
  
  def update_hg(path):
      try:
          import hglib
      except ImportError:
          print("Updating requires python-hglib to be installed.")
          print("Try: pip install python-hglib")
          return -1
      f = open(os.path.join(path, "yt_updater.log"), "a")
      with hglib.open(path) as repo:
          repo.pull(b'https://bitbucket.org/yt_analysis/yt')
          ident = repo.identify().decode("utf-8")
          if "+" in ident:
              print("Changes have been made to the yt source code so I won't ")
              print("update the code. You will have to do this yourself.")
              print("Here's a set of sample commands:")
              print("")
              print("    $ cd %s" % (path))
              print("    $ hg up -C yt  # This will delete any unsaved changes")
              print("    $ %s setup.py develop" % (sys.executable))
              print("")
              return 1
          print("Updating the repository")
          f.write("Updating the repository\n\n")
          books = repo.bookmarks()[0]
          books = [b[0].decode('utf8') for b in books]
          if 'master' in books:
              repo.update('master', check=True)
          else:
              repo.update('yt', check=True)
          f.write("Updated from %s to %s\n\n" % (ident, repo.identify()))
          rebuild_modules(path, f)
      print("Updated successfully.")
  
  def rebuild_modules(path, f):
      f.write("Rebuilding modules\n\n")
      p = subprocess.Popen([sys.executable, "setup.py", "build_ext", "-i"],
                           cwd=path, stdout = subprocess.PIPE,
                           stderr = subprocess.STDOUT)
      stdout, stderr = p.communicate()
      f.write(stdout.decode('utf-8'))
      f.write("\n\n")
      if p.returncode:
          print("BROKEN: See %s" % (os.path.join(path, "yt_updater.log")))
          sys.exit(1)
      f.write("Successful!\n")
  
  
  def get_hg_or_git_version(path):
      if os.path.exists(os.sep.join([path, '.hg'])):
          return get_hg_version(path)
      elif os.path.exists(os.sep.join([path, '.git'])):
          return get_git_version(path)
      return None
  
  def get_git_version(path):
      try:
          import git
      except ImportError:
          print("Updating and precise version information requires ")
          print("gitpython to be installed.")
          print("Try: pip install gitpython")
          return None
      try:
          repo = git.Repo(path)
          return repo.git.rev_parse('HEAD', short=12)
      except git.InvalidGitRepositoryError:
          # path is not a git repository
          return None
  
  def get_hg_version(path):
      try:
          import hglib
      except ImportError:
          print("Updating and precise version information requires ")
          print("python-hglib to be installed.")
          print("Try: pip install python-hglib")
          return None
      try:
          with hglib.open(path) as repo:
              return repo.identify().decode('utf-8')
      except hglib.error.ServerError:
          # path is not an hg repository
          return None
  
  def get_yt_version():
      try:
          from yt.__hg_version__ import hg_version
          return hg_version
      except ImportError:
          pass
      import pkg_resources
      yt_provider = pkg_resources.get_provider("yt")
      path = os.path.dirname(yt_provider.module_path)
      version = get_git_version(path)
      if version is None:
          return version
      else:
          return version[:12].strip().decode('utf-8')
  
  def get_version_stack():
      version_info = {}
      version_info['yt'] = get_yt_version()
      version_info['numpy'] = numpy.version.version
      version_info['matplotlib'] = matplotlib.__version__
      return version_info
  
  def get_script_contents():
      top_frame = inspect.stack()[-1]
      finfo = inspect.getframeinfo(top_frame[0])
      if finfo[2] != "<module>": return None
      if not os.path.exists(finfo[0]): return None
      try:
          contents = open(finfo[0]).read()
      except:
          contents = None
      return contents
  
  def download_file(url, filename):
      requests = get_requests()
      if requests is None:
          return simple_download_file(url, filename)
      else:
          return fancy_download_file(url, filename, requests)
  
  def fancy_download_file(url, filename, requests=None):
      response = requests.get(url, stream=True)
      total_length = response.headers.get('content-length')
  
      with open(filename, 'wb') as fh:
          if total_length is None:
              fh.write(response.content)
          else:
              blocksize = 4 * 1024 ** 2
              iterations = int(float(total_length)/float(blocksize))
  
              pbar = get_pbar(
                  'Downloading %s to %s ' % os.path.split(filename)[::-1],
                  iterations)
              iteration = 0
              for chunk in response.iter_content(chunk_size=blocksize):
                  fh.write(chunk)
                  iteration += 1
                  pbar.update(iteration)
              pbar.finish()
      return filename
  
  def simple_download_file(url, filename):
      class MyURLopener(urllib.request.FancyURLopener):
          def http_error_default(self, url, fp, errcode, errmsg, headers):
              raise RuntimeError("Attempt to download file from %s failed with error %s: %s." % \
                (url, errcode, errmsg))
      fn, h = MyURLopener().retrieve(url, filename)
      return fn
  
  # This code snippet is modified from Georg Brandl
  def bb_apicall(endpoint, data, use_pass = True):
      uri = 'https://api.bitbucket.org/1.0/%s/' % endpoint
      # since bitbucket doesn't return the required WWW-Authenticate header when
      # making a request without Authorization, we cannot use the standard urllib2
      # auth handlers; we have to add the requisite header from the start
      if data is not None:
          data = urllib.parse.urlencode(data)
      req = urllib.request.Request(uri, data)
      if use_pass:
          username = input("Bitbucket Username? ")
          password = getpass.getpass()
          upw = '%s:%s' % (username, password)
          req.add_header('Authorization', 'Basic %s' % base64.b64encode(upw).strip())
      return urllib.request.urlopen(req).read()
  
  def get_yt_supp():
      import hglib
      supp_path = os.path.join(os.environ["YT_DEST"], "src",
                               "yt-supplemental")
      # Now we check that the supplemental repository is checked out.
      if not os.path.isdir(supp_path):
          print()
          print("*** The yt-supplemental repository is not checked ***")
          print("*** out.  I can do this for you, but because this ***")
          print("*** is a delicate act, I require you to respond   ***")
          print("*** to the prompt with the word 'yes'.            ***")
          print()
          response = input("Do you want me to try to check it out? ")
          if response != "yes":
              print()
              print("Okay, I understand.  You can check it out yourself.")
              print("This command will do it:")
              print()
              print("$ hg clone http://bitbucket.org/yt_analysis/yt-supplemental/ ", end=' ')
              print("%s" % (supp_path))
              print()
              sys.exit(1)
          rv = hglib.clone("http://bitbucket.org/yt_analysis/yt-supplemental/", 
                           supp_path)
          if rv:
              print("Something has gone wrong.  Quitting.")
              sys.exit(1)
      # Now we think we have our supplemental repository.
      return supp_path
  
  def fix_length(length, ds):
      registry = ds.unit_registry
      if isinstance(length, YTArray):
          if registry is not None:
              length.units.registry = registry
          return length.in_units("code_length")
      if isinstance(length, numeric_type):
          return YTArray(length, 'code_length', registry=registry)
      length_valid_tuple = isinstance(length, (list, tuple)) and len(length) == 2
      unit_is_string = isinstance(length[1], string_types)
      length_is_number = (isinstance(length[0], numeric_type) and not
                          isinstance(length[0], YTArray))
      if length_valid_tuple and unit_is_string and length_is_number:
          return YTArray(*length, registry=registry)
      else:
          raise RuntimeError("Length %s is invalid" % str(length))
  
  @contextlib.contextmanager
  def parallel_profile(prefix):
      r"""A context manager for profiling parallel code execution using cProfile
  
      This is a simple context manager that automatically profiles the execution
      of a snippet of code.
  
      Parameters
      ----------
      prefix : string
          A string name to prefix outputs with.
  
      Examples
      --------
  
      >>> with parallel_profile('my_profile'):
      ...     yt.PhasePlot(ds.all_data(), 'density', 'temperature', 'cell_mass')
      """
      import cProfile
      from yt.config import ytcfg
      fn = "%s_%04i_%04i.cprof" % (prefix,
                  ytcfg.getint("yt", "__topcomm_parallel_size"),
                  ytcfg.getint("yt", "__topcomm_parallel_rank"))
      p = cProfile.Profile()
      p.enable()
      yield fn
      p.disable()
      p.dump_stats(fn)
  
  def get_num_threads():
      from .config import ytcfg
      nt = ytcfg.getint("yt","numthreads")
      if nt < 0:
          return os.environ.get("OMP_NUM_THREADS", 0)
      return nt
  
  def fix_axis(axis, ds):
      return ds.coordinates.axis_id.get(axis, axis)
  
  def get_image_suffix(name):
      suffix = os.path.splitext(name)[1]
      return suffix if suffix in ['.png', '.eps', '.ps', '.pdf'] else ''
  
  def get_output_filename(name, keyword, suffix):
      r"""Return an appropriate filename for output.
  
      With a name provided by the user, this will decide how to 
      appropriately name the output file by the following rules:
  
      1. if name is None, the filename will be the keyword plus 
         the suffix.
      2. if name ends with "/", assume name is a directory and 
         the file will be named name/(keyword+suffix).  If the
         directory does not exist, first try to create it and
         raise an exception if an error occurs.
      3. if name does not end in the suffix, add the suffix.
      
      Parameters
      ----------
      name : str
          A filename given by the user.
      keyword : str
          A default filename prefix if name is None.
      suffix : str
          Suffix that must appear at end of the filename.
          This will be added if not present.
  
      Examples
      --------
  
      >>> print get_output_filename(None, "Projection_x", ".png")
      Projection_x.png
      >>> print get_output_filename("my_file", "Projection_x", ".png")
      my_file.png
      >>> print get_output_filename("my_file/", "Projection_x", ".png")
      my_file/Projection_x.png
      
      """
      if name is None:
          name = keyword
      name = os.path.expanduser(name)
      if name[-1] == os.sep and not os.path.isdir(name):
          ensure_dir(name)
      if os.path.isdir(name):
          name = os.path.join(name, keyword)
      if not name.endswith(suffix):
          name += suffix
      return name
  
  def ensure_dir_exists(path):
      r"""Create all directories in path recursively in a parallel safe manner"""
      my_dir = os.path.dirname(path)
      # If path is a file in the current directory, like "test.txt", then my_dir
      # would be an empty string, resulting in FileNotFoundError when passed to
      # ensure_dir. Let's avoid that.
      if my_dir:
          ensure_dir(my_dir)
  
  def ensure_dir(path):
      r"""Parallel safe directory maker."""
      if os.path.exists(path):
          return path
  
      try:
          os.makedirs(path)
      except OSError as e:
          if e.errno == errno.EEXIST:
              pass
          else:
              raise
      return path
  
  def validate_width_tuple(width):
      if not iterable(width) or len(width) != 2:
          raise YTInvalidWidthError(
              "width (%s) is not a two element tuple" % width)
      is_numeric = isinstance(width[0], numeric_type)
      length_has_units = isinstance(width[0], YTArray)
      unit_is_string = isinstance(width[1], string_types)
      if not is_numeric or length_has_units and unit_is_string:
          msg = "width (%s) is invalid. " % str(width)
          msg += "Valid widths look like this: (12, 'au')"
          raise YTInvalidWidthError(msg)
  
  _first_cap_re = re.compile('(.)([A-Z][a-z]+)')
  _all_cap_re = re.compile('([a-z0-9])([A-Z])')
  
  @lru_cache(maxsize=128, typed=False)
  def camelcase_to_underscore(name):
      s1 = _first_cap_re.sub(r'\1_\2', name)
      return _all_cap_re.sub(r'\1_\2', s1).lower()
  
  def set_intersection(some_list):
      if len(some_list) == 0: return set([])
      # This accepts a list of iterables, which we get the intersection of.
      s = set(some_list[0])
      for l in some_list[1:]:
          s.intersection_update(l)
      return s
  
  @contextlib.contextmanager
  def memory_checker(interval = 15, dest = None):
      r"""This is a context manager that monitors memory usage.
  
      Parameters
      ----------
      interval : int
          The number of seconds between printing the current memory usage in
          gigabytes of the current Python interpreter.
  
      Examples
      --------
  
      >>> with memory_checker(10):
      ...     arr = np.zeros(1024*1024*1024, dtype="float64")
      ...     time.sleep(15)
      ...     del arr
      """
      import threading
      if dest is None:
          dest = sys.stdout
      class MemoryChecker(threading.Thread):
          def __init__(self, event, interval):
              self.event = event
              self.interval = interval
              threading.Thread.__init__(self)
  
          def run(self):
              while not self.event.wait(self.interval):
                  print("MEMORY: %0.3e gb" % (get_memory_usage()/1024.), file=dest)
  
      e = threading.Event()
      mem_check = MemoryChecker(e, interval)
      mem_check.start()
      try:
          yield
      finally:
          e.set()
  
  
  def deprecated_class(cls):
      @wraps(cls)
      def _func(*args, **kwargs):
          # Note we use SyntaxWarning because by default, DeprecationWarning is
          # not shown.
          warnings.warn(
              "This usage is deprecated.  Please use %s instead." % cls.__name__,
              SyntaxWarning, stacklevel=2)
          return cls(*args, **kwargs)
      return _func
  
  def enable_plugins():
      """Forces the plugins file to be parsed.
  
      This plugin file is a means of creating custom fields, quantities,
      data objects, colormaps, and other code classes and objects to be used
      in yt scripts without modifying the yt source directly.
  
      The file must be located at ``$HOME/.config/yt/my_plugins.py``.
  
      Warning: when you use this function, your script will only be reproducible
      if you also provide the ``my_plugins.py`` file.
      """
      import yt
      from yt.fields.my_plugin_fields import my_plugins_fields
      from yt.config import ytcfg, CONFIG_DIR
      my_plugin_name = ytcfg.get("yt", "pluginfilename")
  
      # In the following order if pluginfilename is: an absolute path, located in
      # the CONFIG_DIR, located in an obsolete config dir.
      _fn = None
      old_config_dir = os.path.join(os.path.expanduser('~'), '.yt')
      for base_prefix in ('', CONFIG_DIR, old_config_dir):
          if os.path.isfile(os.path.join(base_prefix, my_plugin_name)):
              _fn = os.path.join(base_prefix, my_plugin_name)
              break
  
      if _fn is not None and os.path.isfile(_fn):
          if _fn.startswith(old_config_dir):
              mylog.warn(
                  'Your plugin file is located in a deprecated directory. '
                  'Please move it from %s to %s',
                  os.path.join(old_config_dir, my_plugin_name),
                  os.path.join(CONFIG_DIR, my_plugin_name))
          mylog.info("Loading plugins from %s", _fn)
          ytdict = yt.__dict__
          execdict = ytdict.copy()
          execdict['add_field'] = my_plugins_fields.add_field
          localdict = {}
          with open(_fn) as f:
              code = compile(f.read(), _fn, 'exec')
              exec(code, execdict, localdict)
          ytnamespace = list(ytdict.keys())
          for k in localdict.keys():
              if k not in ytnamespace:
                  if callable(localdict[k]):
                      setattr(yt, k, localdict[k])
  
  def fix_unitary(u):
      if u == '1':
          return 'unitary'
      else:
          return u
  
  def get_hash(infile, algorithm='md5', BLOCKSIZE=65536):
      """Generate file hash without reading in the entire file at once.
  
      Original code licensed under MIT.  Source:
      http://pythoncentral.io/hashing-files-with-python/
  
      Parameters
      ----------
      infile : str
          File of interest (including the path).
      algorithm : str (optional)
          Hash algorithm of choice. Defaults to 'md5'.
      BLOCKSIZE : int (optional)
          How much data in bytes to read in at once.
  
      Returns
      -------
      hash : str
          The hash of the file.
  
      Examples
      --------
      >>> import yt.funcs as funcs
      >>> funcs.get_hash('/path/to/test.png')
      'd38da04859093d430fa4084fd605de60'
  
      """
      import hashlib
  
      try:
          hasher = getattr(hashlib, algorithm)()
      except:
          raise NotImplementedError("'%s' not available!  Available algorithms: %s" %
                                    (algorithm, hashlib.algorithms))
  
      filesize   = os.path.getsize(infile)
      iterations = int(float(filesize)/float(BLOCKSIZE))
  
      pbar = get_pbar('Generating %s hash' % algorithm, iterations)
  
      iter = 0
      with open(infile,'rb') as f:
          buf = f.read(BLOCKSIZE)
          while len(buf) > 0:
              hasher.update(buf)
              buf = f.read(BLOCKSIZE)
              iter += 1
              pbar.update(iter)
          pbar.finish()
  
      return hasher.hexdigest()
  
  def get_brewer_cmap(cmap):
      """Returns a colorbrewer colormap from palettable"""
      try:
          import brewer2mpl
      except ImportError:
          brewer2mpl = None
      try:
          import palettable
      except ImportError:
          palettable = None
      if palettable is not None:
          bmap = palettable.colorbrewer.get_map(*cmap)
      elif brewer2mpl is not None:
          warnings.warn("Using brewer2mpl colormaps is deprecated. "
                        "Please install the successor to brewer2mpl, "
                        "palettable, with `pip install palettable`. "
                        "Colormap tuple names remain unchanged.")
          bmap = brewer2mpl.get_map(*cmap)
      else:
          raise RuntimeError(
              "Please install palettable to use colorbrewer colormaps")
      return bmap.get_mpl_colormap(N=cmap[2])
  
  def get_requests():
      try:
          import requests
      except ImportError:
          requests = None
      return requests
  
  @contextlib.contextmanager
  def dummy_context_manager(*args, **kwargs):
      yield
  
  def matplotlib_style_context(style_name=None, after_reset=False):
      """Returns a context manager for controlling matplotlib style.
  
      Arguments are passed to matplotlib.style.context() if specified. Defaults
      to setting "classic" style, after resetting to the default config parameters.
  
      On older matplotlib versions (<=1.5.0) where matplotlib.style isn't
      available, returns a dummy context manager.
      """
      if style_name is None:
          style_name = {
              'mathtext.fontset': 'cm',
              'mathtext.fallback_to_cm': True,
          }
      try:
          import matplotlib.style
          return matplotlib.style.context(style_name, after_reset=after_reset)
      except ImportError:
          pass
      return dummy_context_manager()
  
  interactivity = False
  
  """Sets the condition that interactive backends can be used."""
  def toggle_interactivity():
      global interactivity
      interactivity = not interactivity
      if interactivity is True:
          if '__IPYTHON__' in dir(builtins):
              import IPython
              shell = IPython.get_ipython()
              shell.magic('matplotlib')
          else:
              import matplotlib
              matplotlib.interactive(True)
  
  def get_interactivity():
      return interactivity
  
  def setdefaultattr(obj, name, value):
      """Set attribute with *name* on *obj* with *value* if it doesn't exist yet
  
      Analogous to dict.setdefault
      """
      if not hasattr(obj, name):
          setattr(obj, name, value)
      return getattr(obj, name)
  
  def parse_h5_attr(f, attr):
      """A Python3-safe function for getting hdf5 attributes.
  
      If an attribute is supposed to be a string, this will return it as such.
      """
      val = f.attrs.get(attr, None)
      if isinstance(val, bytes):
          return val.decode('utf8')
      else:
          return val
  
  def issue_deprecation_warning(msg, stacklevel=3):
      from numpy import VisibleDeprecationWarning
      warnings.warn(msg, VisibleDeprecationWarning, stacklevel=stacklevel)
  
  def obj_length(v):
      if iterable(v):
          return len(v)
      else:
          # If something isn't iterable, we return 0 
          # to signify zero length (aka a scalar).
          return 0
  
  def handle_mks_cgs(values, field_units):
      try:
          values = values.to(field_units)
      except YTEquivalentDimsError as e:
          values = values.to_equivalent(e.new_units, e.base)
      return values
  
  def validate_3d_array(obj):
      if not iterable(obj) or len(obj) != 3:
          raise TypeError("Expected an array of size (3,), received '%s' of "
                          "length %s" % (str(type(obj)).split("'")[1], len(obj)))
  
  def validate_float(obj):
      """Validates if the passed argument is a float value.
  
      Raises an exception if `obj` is a single float value
      or a YTQunatity of size 1.
  
      Parameters
      ----------
      obj : Any
          Any argument which needs to be checked for a single float value.
  
      Raises
      ------
      TypeError
          Raised if `obj` is not a single float value or YTQunatity
  
      Examples
      --------
      >>> validate_float(1)
      >>> validate_float(1.50)
      >>> validate_float(YTQuantity(1,"cm"))
      >>> validate_float((1,"cm"))
      >>> validate_float([1, 1, 1])
      Traceback (most recent call last):
      ...
      TypeError: Expected a numeric value (or size-1 array), received 'list' of length 3
  
      >>> validate_float([YTQuantity(1, "cm"), YTQuantity(2,"cm")])
      Traceback (most recent call last):
      ...
      TypeError: Expected a numeric value (or size-1 array), received 'list' of length 2
      """
      if isinstance(obj, tuple):
          if len(obj) != 2 or not isinstance(obj[0], numeric_type)\
                  or not isinstance(obj[1], string_types):
              raise TypeError("Expected a numeric value (or tuple of format "
                              "(float, String)), received an inconsistent tuple "
                              "'%s'." % str(obj))
          else:
              return
      if iterable(obj) and (len(obj) != 1 or not isinstance(obj[0], numeric_type)):
          raise TypeError("Expected a numeric value (or size-1 array), "
                          "received '%s' of length %s"
                          % (str(type(obj)).split("'")[1], len(obj)))
  
  
  def validate_iterable(obj):
      if obj is not None and not iterable(obj):
          raise TypeError("Expected an iterable object,"
                          " received '%s'" % str(type(obj)).split("'")[1])
  
  def validate_object(obj, data_type):
      if obj is not None and not isinstance(obj, data_type):
          raise TypeError("Expected an object of '%s' type, received '%s'"
                          % (str(data_type).split("'")[1],
                          str(type(obj)).split("'")[1]))
  
  def validate_axis(ds, axis):
      if ds is not None:
          valid_axis = ds.coordinates.axis_name.keys()
      else:
          valid_axis = [0, 1, 2, 'x', 'y', 'z', 'X', 'Y', 'Z']
      if axis not in valid_axis:
          raise TypeError("Expected axis of int or char type (can be %s), "
                          "received '%s'." % (list(valid_axis), axis))
  
  def validate_center(center):
      if isinstance(center, string_types):
          c = center.lower()
          if c not in ["c", "center", "m", "max", "min"] \
                  and not c.startswith("max_") and not c.startswith("min_"):
              raise TypeError("Expected 'center' to be in ['c', 'center', "
                              "'m', 'max', 'min'] or the prefix to be "
                              "'max_'/'min_', received '%s'." % center)
      elif not isinstance(center, (numeric_type, YTQuantity)) \
              and not iterable(center):
          raise TypeError("Expected 'center' to be a numeric object of type "
                          "list/tuple/np.ndarray/YTArray/YTQuantity, "
                          "received '%s'." % str(type(center)).split("'")[1])
  