read_csv: if parse_dates dont appear in use_cols, we get a trace (original) (raw)

Code Sample, a copy-pastable example if possible

Your code here

import pandas as pd import io

content = io.StringIO(''' time,val 212.23, 32 ''')

date_cols = ['time']

df = pd.read_csv( content, sep=',', usecols=['val'], dtype= { 'val': int }, parse_dates=date_cols, )

Problem description

triggers

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    parse_dates=date_cols,
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 685, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 463, in _read
    data = parser.read(nrows)
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 1154, in read
    ret = self._engine.read(nrows)
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 2134, in read
    names, data = self._do_date_conversions(names, data)
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 1885, in _do_date_conversions
    keep_date_col=self.keep_date_col,
  File "/nix/store/k4fd48jzsyafvcifa6wi6pk4vaprnw36-python3.7-pandas-0.25.3/lib/python3.7/site-packages/pandas/io/parsers.py",
line 3335, in _process_date_conversion
    data_dict[colspec] = converter(data_dict[colspec])
KeyError: 'time'

i.e., if you use columns in parse_dates that dont appear in use_cols, then you are screwed.

Either parse_dates sould be added to use_cols or the documentation precise it. An assert could make the error more understandable too.
pandas 0.25.3