title: Numpy datetime format
body: <p>First time post - I'm following a Data Analysis with Python Introduction course in Lynda.com. The instructor in the video is using Jupiter Notebooks, I am using Visual Studio Code to follow along but I've hit a snag with the following:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as pp
  import seaborn
  import urllib
  
  def findstation(s):
      found = {code: name for code, name in stations.items() if s in name}
      print(found)
  
  def parsefile(filename):
      return np.genfromtxt(filename,
                              delimiter = dly_delimiter,
                              usecols = dly_usecols,
                              dtype = dly_dtype,
                              names = dly_names)
  
  dly_delimiter = [11,4,2,4] + [5,1,1,1] * 31
  dly_usecols = [1,2,3] + [4*i for i in range(1, 32)]
  dly_dtype = [np.int32, np.int32, (np.str_, 4)] + [np.int32]*31
  dly_names = ['year', 'month', 'obs'] + [str(day) for day in range(1,31+1)]
  
  def unroll(record):
      startdate = np.datetime64('{}-{:02}'.format(record['year'],record['month']))
      dates = np.arange(startdate, startdate + np.timedelta64(1, 'M'), np.timedelta64(1, 'D'))
      rows = [(date, record[str(i+1)]) for i,date in enumerate(dates)]
      return rows
  
  #urllib.request.urlretrieve('ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/daily/ghcnd-stations.txt', 'stations.txt')
  lines = open('stations.txt','r').readlines()[:10]
  #print(lines)
  
  stations = {}
  
  for line in open('stations.txt','r'):
      if "GSN" in line:
          fields = line.split()
          stations[fields[0]] = ' '.join(fields[4:])
  
  print(len(stations))
  #findstation('LIHUE')
  #findstation('SAN DIEGO')
  #findstation('MINNEAPOLIS')
  #findstation('IRKUTSK')
  
  datastations = ['USW00022536', 'USW00023188', 'USW00014922', 'RSM00030710']
  
  daily = open('USW00022536.dly', 'r').readlines()[:10]
  #print(daily)
  lihue = parsefile('USW00022536.dly')
  u_lihue = unroll(lihue)
  print(u_lihue)
  </code></pre>
  
  <p>The following error message displays:</p>
  
  <pre class="lang-none prettyprint-override"><code>line 23, in unroll startdate = np.datetime64('{}-{:02}'.format(record['year'],record['month']))
  TypeError: unsupported format string passed to numpy.ndarray.__format__
  </code></pre>
  
  <p>The code works using Jupiter Notebooks - thoughts?</p>