class_docstr: Store a sequence of fields, reading multipart/form-data.
  
  This class provides naming, typing, files stored on disk, and
  more.  At the top level, it is accessible like a dictionary, whose
  keys are the field names.  (Note: None can occur as a field name.)
  The items are either a Python list (if there's multiple values) or
  another FieldStorage or MiniFieldStorage object.  If it's a single
  object, it has the following attributes:
  
  name: the field name, if specified; otherwise None
  
  filename: the filename, if specified; otherwise None; this is the
      client side filename, *not* the file name on which it is
      stored (that's a temporary file you don't deal with)
  
  value: the value as a *string*; for file uploads, this
      transparently reads the file every time you request the value
      and returns *bytes*
  
  file: the file(-like) object from which you can read the data *as
      bytes* ; None if the data is stored a simple string
  
  type: the content-type, or None if not specified
  
  type_options: dictionary of options specified on the content-type
      line
  
  disposition: content-disposition, or None if not specified
  
  disposition_options: dictionary of corresponding options
  
  headers: a dictionary(-like) object (sometimes email.message.Message or a
      subclass thereof) containing *all* headers
  
  The class is subclassable, mostly for the purpose of overriding
  the make_file() method, which is called internally to come up with
  a file open for reading and writing.  This makes it possible to
  override the default choice of storing all files in a temporary
  directory and unlinking them as soon as they have been opened.
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docstr: Dictionary style len(x) support.
docstr_tok: ["Dictionary","style","len","(","x",")","support","."]
code: def __len__(self):
      """Dictionary style len(x) support."""
      return len(self.keys())
  
imports: from io import StringIO, BytesIO, TextIOWrapper
  from collections.abc import Mapping
  import sys
  import os
  import urllib.parse
  from email.parser import FeedParser
  from email.message import Message
  import html
  import locale
  import tempfile
  import warnings
label_desc: Use image node_id 14 for calling the FieldStorage obj's underlying member method code with example usage: obj.__len__() and returns: len