flake8-string-format 0.2.1

string format checker, plugin for flake8

An extension for flake8 to check the strings and parameters using str.format. It checks all strings whether they use numbered parameters with an implicit index which isn’t support in Python 2.6.

In all instances of '…'.format(…) it will also check whether there are enough parameters given. If the format call uses variable arguments, it’ll just check whether the right types of arguments are present.

Standalone script

The checker can be used directly:

$ python -m flake8_string_format some_file.py
some_file.py:1:1: P101 format string does contain unindexed parameters

Even though flake8 still uses optparse this script in standalone mode is using argparse.

Plugin for Flake8

When both flake8 2.0 and flake8-string-format are installed, the plugin is available in flake8:

$ flake8 --version
2.0 (pep8: 1.4.2, flake8-string-format: 0.2.0, pyflakes: 0.6.1)

Via --ignore it’s possible to ignore unindxed parameters:

$ flake8 some_file.py
...
some_file.py:1:1: P101 format string does contain unindexed parameters

$ flake8 --ignore P101 some_file.py
...

Parameters

This module doesn’t add any additional parameters. The stand alone version also mimics flake8’s ignore parameter.

Error codes

This plugin is using the following error codes:

Presence of implicit parameters
P101	format string does contain unindexed parameters
P102	docstring does contain unindexed parameters
P103	other string does contain unindexed parameters
Missing values in the parameters
P201	format call uses to large index (INDEX)
P202	format call uses missing keyword (KEYWORD)
P203	format call uses keyword arguments but no named entries
P204	format call uses variable arguments but no numbered entries
P205	format call uses implicit and explicit indexes together
Unused values in the parameters
P301	format call provides unused index (INDEX)
P302	format call provides unused keyword (KEYWORD)

Operation

The plugin will go through all bytes, str and unicode instances. If it encounters bytes instances on Python 3, it’ll decode them using ASCII and if that fails it’ll skip that entry.

The strings are basically sorted into three types corresponding to the P1XX range. Only the format string can cause all errors while any other string can only cause the corresponding P1XX error.

For this plugin all strings which are the first expression of the module or after a function or class defnition are considered docstrings.

If the format method is used on a string or str.format with the string as the first parameter, it will consider this a format string and will analyze the parameters of that call. If that call uses variable arguments, it cannot issue P201 and P202 as missing entries might be hidden in those variable arguments. P301 and P302 can still be checked for any argument which is defined statically.

Python 2.6 support

Python 2.6 is only partially supported as it’s using Python’s capability to format a string. So if a string contains implicit parameters, it won’t be detected as a parameter on Python 2.6 and thus it won’t cause any P1XX errors. But it might still cause an error P301 when variable arguments aren’t used.

So if Python 2.6 compatibility is wished and thus implicit parameters aren’t allowed, this plugin won’t cause false positives.

Changes

0.2.1 - 2015-09-20

• Support str.format("…", …) calls and handle them like "…".format(…)

0.2.0 - 2015-09-12

• Instead of using a regex it’s trying to parse it using Python’s parser

• This result can also be used now to verify that enough parameters are given

• Limited Python 2.6 support

0.1.0 - 2015-09-10

• Detect unindexed parameters in all strings

• Separate error code for docstrings