BUG: read_csv with both names and parse_date raises 'NoneType' TypeError

[quazgar]

This is probably similar to #14792, but still happens with 0.23.3 (a friend even tested it with 1.0.3).

Testcase

import io
s = """A,B,\n1,2"""
pd.read_csv(io.StringIO(s), parse_dates=["B"], names=["B"])

raises:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-146-082b3d7afa0a> in <module>()
      1 import io
      2 s = """A,B,\n1,2"""
----> 3 pd.read_csv(io.StringIO(s), parse_dates=["B"], names=["B"])

/usr/lib/python3/dist-packages/pandas/io/parsers.py in parser_f(filepath_or_buffer, sep, delimiter, header, names, index_col, usecols, squeeze, prefix, mangle_dupe_cols, dtype, engine, converters, true_values, false_values, skipinitialspace, skiprows, nrows, na_values, keep_default_na, na_filter, verbose, skip_blank_lines, parse_dates, infer_datetime_format, keep_date_col, date_parser, dayfirst, iterator, chunksize, compression, thousands, decimal, lineterminator, quotechar, quoting, escapechar, comment, encoding, dialect, tupleize_cols, error_bad_lines, warn_bad_lines, skipfooter, doublequote, delim_whitespace, low_memory, memory_map, float_precision)
    676                     skip_blank_lines=skip_blank_lines)
    677
--> 678         return _read(filepath_or_buffer, kwds)
    679
    680     parser_f.__name__ = name

/usr/lib/python3/dist-packages/pandas/io/parsers.py in _read(filepath_or_buffer, kwds)
    444
    445     try:
--> 446         data = parser.read(nrows)
    447     finally:
    448         parser.close()

/usr/lib/python3/dist-packages/pandas/io/parsers.py in read(self, nrows)
   1034                 raise ValueError('skipfooter not supported for iteration')
   1035
-> 1036         ret = self._engine.read(nrows)
   1037
   1038         # May alter columns / col_dict

/usr/lib/python3/dist-packages/pandas/io/parsers.py in read(self, nrows)
   1887
   1888                 values = self._maybe_parse_dates(values, i,
-> 1889                                                  try_parse_dates=True)
   1890                 arrays.append(values)
   1891

/usr/lib/python3/dist-packages/pandas/io/parsers.py in _maybe_parse_dates(self, values, index, try_parse_dates)
   1946
   1947     def _maybe_parse_dates(self, values, index, try_parse_dates=True):
-> 1948         if try_parse_dates and self._should_parse_dates(index):
   1949             values = self._date_conv(values)
   1950         return values

/usr/lib/python3/dist-packages/pandas/io/parsers.py in _should_parse_dates(self, i)
   1319             else:
   1320                 name = None
-> 1321             j = self.index_col[i]
   1322
   1323             if is_scalar(self.parse_dates):

TypeError: 'NoneType' object is not subscriptable

Notes

This does not happen with engine="python" (you only get a ParseError there).

[siddartha-RE]

In Pandas 1.0.3 I am seeing the error with the following simple invoication:

df = pd.read_csv('/tmp/csv_no_dates.csv', nrows=500, low_memory=False, parse_dates=[])

Bottom of stack:

  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 676, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 454, in _read
    data = parser.read(nrows)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 1133, in read
    ret = self._engine.read(nrows)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 2080, in read
    values = self._maybe_parse_dates(values, i, try_parse_dates=True)
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 2141, in _maybe_parse_dates
    if try_parse_dates and self._should_parse_dates(index):
  File "/usr/local/lib/python3.6/dist-packages/pandas/io/parsers.py", line 1448, in _should_parse_dates
    j = self.index_col[i]