Use the code formatter Black for tsfresh

[mendel5]

While working with tsfresh I've noticed that in some parts of the code, documentation, etc. single quotes (') are used while in other parts double quotes (") are used.

Examples:

• Single quotes in the example notebook 01 Feature Extraction and Selection.ipynb
• Double quotes in the example notebook04 Multiclass Selection Example.ipynb

The PEP 8 -- Style Guide for Python Code at https://www.python.org/dev/peps/pep-0008/#string-quotes says this:

In Python, single-quoted strings and double-quoted strings are the same. This PEP does not make a recommendation for this. Pick a rule and stick to it. When a string contains single or double quote characters, however, use the other one to avoid backslashes in the string. It improves readability.

The Comprehensive Knowledge Archive Network (CKAN) has a recommendation at https://docs.ckan.org/en/latest/contributing/python.html#use-single-quotes:

Use single-quotes for string literals, but use double-quotes for strings that are likely to contain single-quote characters as part of the string itself (such as error messages, or any strings containing natural language).

Single-quotes are easier to read and to type, but if a string contains single-quote characters then double-quotes are better than escaping the single-quote characters or wrapping the string in double single-quotes.

The same standards could be applied to docstrings, see PEP 257 -- Docstring Conventions at https://www.python.org/dev/peps/pep-0257/.

CKAN also has a recommendation for docstrings at https://docs.ckan.org/en/latest/contributing/python.html#pep-257-docstring-conventions:

We use '''triple single quotes''' around docstrings, not """triple double quotes""".

I can submit a pull request.

[nils-braun]

I appreciate your idea on having a common style in the code.

To be fair, using a common quote style is not super usual in python projects (see e.g. numpy) - but we can do this nevertheless - I do not have hard feelings against it.

What I would recommend however is to use as much automation as possible to make it easier for developers to stick with the standard we chose (for example, I am working with a German keyboard where the " is easier to reach than the ' - at least on my keyboard). So I would propose to maybe go with a tool like "black" (as was suggested e.g. in #607) and add it to both the CI pipeline as well as the contribution guidelines.
(black, by the way prefers double quotes).

Just out of curiosity: I worked with several open and close source python applications so far, but I have barely never seen single quotes used for docstrings - also because PEP-257 uses double quotes. Do you know a reason why single triple quotes were chosen?

[MaxBenChrist]

Maybe we could add pylint with the following add-on https://github.com/edaniszewski/pylint-quotes to check this in the CI pipeline

[mendel5]

Related to #858

@nils-braun I finally found the time to start working on this, see #858

[mendel5]

New pull request with the python package "black" applied to the tsfresh repository:

• Apply python package "black" to tsfresh repo #871

[mendel5]

I have renamed this issue to better reflect the changes that were made.

Old name:

Adopt CKAN Python coding standards: Use single quotes instead of double quotes

New name:

Use the code formatter Black for tsfresh

https://github.com/psf/black

[nils-braun]

Well done and well documented!

[mendel5]

Thanks! 🎉