code: def ensure_timezone(func, argname, arg):
      """Argument preprocessor that converts the input into a tzinfo object.
  
      Examples
      --------
      >>> from zipline.utils.preprocess import preprocess
      >>> @preprocess(tz=ensure_timezone)
      ... def foo(tz):
      ...     return tz
      >>> foo('utc')
      <UTC>
      """
      if isinstance(arg, tzinfo):
          return arg
      if isinstance(arg, string_types):
          return timezone(arg)
  
      raise TypeError(
          "{func}() couldn't convert argument "
          "{argname}={arg!r} to a timezone.".format(
              func=_qualified_name(func),
              argname=argname,
              arg=arg,
          ),
      )
  
imports: from datetime import tzinfo
  from functools import partial
  from operator import attrgetter
  from numpy import dtype
  import pandas
  from pytz import timezone
  from six import iteritems, string_types, PY3
  from toolz import valmap, complement, compose
  import toolz.curried.operator
  from zipline.utils.compat import wraps
  from zipline.utils.functional import getattrs
  from zipline.utils.preprocess import call, preprocess
label_desc: Use image node_id 5 for calling a global function with example usage: ensure_timezone(func, argname, arg) and returns: arg, timezone