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DOC: Improved the docstring of errors.ParserWarning #20076

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Merged
merged 8 commits into from
Mar 15, 2018
Merged

DOC: Improved the docstring of errors.ParserWarning #20076

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abdc710
DOC: Improved the docstring of errors.ParserWarning
joaoavf Mar 9, 2018
0607602
Correcting whitespace issue on line 58
joaoavf Mar 9, 2018
850a3fe
Converting the short summary to one line.
joaoavf Mar 9, 2018
815bf0e
minor formatting changes
joaoavf Mar 9, 2018
b12907e
Added a 'See Also' section
joaoavf Mar 9, 2018
8fe1c04
Making changes request by jreback and minor formatting changes
joaoavf Mar 10, 2018
37c9f96
Adding the default 'c' parser to the short summary
joaoavf Mar 10, 2018
17687b5
Pass doctests [ci skip]
TomAugspurger Mar 15, 2018
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42 changes: 38 additions & 4 deletions pandas/errors/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,44 @@ class EmptyDataError(ValueError):

class ParserWarning(Warning):
"""
Warning that is raised in `pd.read_csv` whenever it is necessary
to change parsers (generally from 'c' to 'python') contrary to the
one specified by the user due to lack of support or functionality for
parsing particular attributes of a CSV file with the requested engine.
Warning raised when reading a file that doesn't use the default 'c' parser.

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The first line needs to fit in a line. Can you write something more concise please? This paragraph is really useful, and it surely needs to be in the description, but the first line is used in some summaries that should be shorter. Something like Warning raised when reading a table does not use the default parser. Not sure if it's accurate or fits in one line, but to give you an idea.

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Great Mark! Thanks for the suggestion. Already commited my version of it.

Raised by `pd.read_csv` and `pd.read_table` when it is necessary to change
parsers, generally from the default 'c' parser to 'python'.

It happens due to a lack of support or functionality for parsing a
particular attribute of a CSV file with the requested engine.

Currently, 'c' unsupported options include the following parameters:

1. `sep` other than a single character (e.g. regex separators)
2. `skipfooter` higher than 0
3. `sep=None` with `delim_whitespace=False`

The warning can be avoided by adding `engine='python'` as a parameter in
`pd.read_csv` and `pd.read_table` methods.

See Also
--------
pd.read_csv : Read CSV (comma-separated) file into DataFrame.
pd.read_table : Read general delimited file into DataFrame.

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I think read_csv and read_table are good candidates for a See Also section, as you're mentioning them.

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Added a See Also section with read_csv and read_table.

Examples
--------
Using a `sep` in `pd.read_csv` other than a single character:

>>> import io
>>> csv = u'''a;b;c
... 1;1,8
... 1;2,1'''
>>> df = pd.read_csv(io.StringIO(csv), sep='[;,]')
Traceback (most recent call last):
...
ParserWarning: Falling back to the 'python' engine...
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did you check why the validation says that this test didn't pass, and that the read_csv returned nothing?

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@joaoavf joaoavf Mar 9, 2018 •
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When I ran the code in my console I had this warning displayed: 'ParserWarning: Falling back to the 'python' engine...'

I thought it might have something to do as it is a warning and not an error. Something along the lines that the kind of output generated by an error could be caught by Traceback but not the output of a warning.

Any ideas on how to fix and approach this?


Adding `engine='python'` to `pd.read_csv` removes the Warning:

>>> df = pd.read_csv(io.StringIO(csv), sep='[;,]', engine='python')
"""


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