Concurrently detect the minimum Python versions needed to run code





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Concurrently detect the minimum Python versions needed to run code. Additionally, since the code is vanilla Python, and it doesn't have any external dependencies, it works with v2.7+ and v3+.

It functions by parsing Python code into an abstract syntax tree (AST), which it traverses and matches against internal dictionaries with 3223 rules, covering v2.0-2.7 and v3.0-3.9, divided into 139 modules, 2247 classes/functions/constants members of modules, 713 kwargs of functions, 4 strftime directives, 3 bytes format directives, 2 array typecodes, 3 codecs error handler names, 20 codecs encodings, 75 builtin generic annotation types, 8 builtin dict union (|) types, 7 builtin dict union merge (|=) types, and 2 user function decorators.

Backports of the standard library, like typing, can be enabled for better results.

The project is fairly well-tested with 3538 unit and integration tests that are executed on Linux, macOS, and Windows.

It is recommended to use the most recent Python version to run Vermin on projects since Python's own language parser is used to detect language features, like f-strings since Python 3.6 etc.


It is fairly straightforward to use Vermin::

./ /path/to/your/project

Or via PyPi <>__::

% pip install vermin % vermin /path/to/your/project

Arch Linux (AUR) <>__::

% yay -S python-vermin

Spack <> (pkg <>)::

% git clone % . spack/share/spack/ # depending on shell % spack install py-vermin % spack load py-vermin

When using continuous integration (CI) tools, like Travis CI <>_, Vermin can be used to check that the minimum required versions didn't change. The following is an excerpt::


  • ./
  • pip install vermin script:
  • vermin -t=2.7 -t=3 project_package


Features detected include v2/v3 print expr and print(expr), long, f-strings, coroutines (async and await), asynchronous generators (await and yield in same function), asynchronous comprehensions, await in comprehensions, asynchronous for-loops, boolean constants, named expressions, keyword-only parameters, positional-only parameters, nonlocal, yield from, exception context cause (raise .. from ..), set literals, set comprehensions, dict comprehensions, infix matrix multiplication, "..".format(..), imports (import X, from X import Y, from X import *), function calls wrt. name and kwargs, strftime + strptime directives used, function and variable annotations (also Final and Literal), continue in finally block, modular inverse pow(), array typecodes, codecs error handler names, encodings, % formatting and directives for bytes and bytearray, with statement, multiple context expressions in a with statement, unpacking assignment, generalized unpacking, ellipsis literal (...) out of slices, dictionary union ({..} | {..}), dictionary union merge (a = {..}; a |= {..}), builtin generic type annotations (list[str]), function decorators, class decorators and relaxed decorators. It tries to detect and ignore user-defined functions, classes, arguments, and variables with names that clash with library-defined symbols.


Self-documenting fstrings detection has been disabled by default because the built-in AST cannot distinguish f'{a=}' from f'a={a}', for instance, since it optimizes some information away (#39 <>__). And this incorrectly marks some source code as using fstring self-doc when only using general fstring. To enable (unstable) fstring self-doc detection, use --feature fstring-self-doc.

Function and variable annotations aren't evaluated at definition time when from __future__ import annotations is used (PEP 563 <>). This is why --no-eval-annotations is on by default (since v1.1.1, #66 <>). If annotations are being evaluated at runtime, like using typing.get_type_hints or evaluating __annotations__ of an object, --eval-annotations should be used for best results.

Configuration file

Vermin automatically tries to detect a config file, starting in the current working directory where it is run, following parent folders until either the root or project boundary files/folders are reached. However, if --config-file is specified, no config is auto-detected and loaded.

Config file names being looked for: vermin.ini, vermin.conf, .vermin, setup.cfg

Project boundary files/folders: .git, .svn, .hg, .bzr, _darcs, .fslckout

A sample config file can be found here <sample.vermin.ini>__.

Note that Vermin config can be in the same INI file as other configs, like the commonly used setup.cfg:

.. code-block:: ini

[vermin] verbose = 1 processes = 4

[flake8] ignore = E111,F821


.. code-block:: console

% ./ -q vermin Minimum required versions: 2.7, 3.0

% ./ -q -t=3.3 vermin Minimum required versions: 2.7, 3.0 Target versions not met: 3.3 % echo $? 1

% ./ -q --versions vermin Minimum required versions: 2.7, 3.0 Version range: 2.0, 2.6, 2.7, 3.0

% ./ -v examples Detecting python files.. Analyzing 6 files using 8 processes.. /path/to/examples/ 2.7, 3.2 /path/to/examples/ 2.7, 3.0 /path/to/examples/ 2.0, 3.0 /path/to/examples/ !2, 3.4 /path/to/examples/ /path/to/examples/ Minimum required versions: 3.4 Incompatible versions: 2

% ./ -vv /path/to/examples/ Detecting python files.. Analyzing using 8 processes.. !2, 3.4 /path/to/examples/ 'abc' requires 2.6, 3.0 'abc.ABC' requires !2, 3.4

Minimum required versions: 3.4 Incompatible versions: 2

% ./ -vvv /path/to/examples/ Detecting python files.. Analyzing using 8 processes.. !2, 3.4 /path/to/examples/ L1 C7: 'abc' requires 2.6, 3.0 L2: 'abc.ABC' requires !2, 3.4

Minimum required versions: 3.4 Incompatible versions: 2

% ./ -f parsable /path/to/examples/ /path/to/examples/'abc' module /path/to/examples/!2:3.4:'abc.ABC' member /path/to/examples/!2:3.4: :::!2:3.4:

Linting: Showing only target versions violations

Vermin shows lots of useful minimum version results when run normally, but it can also be used as a linter to show only rules violating specified target versions by using --violations and one or two --target values. Verbosity level 2 is automatically set when showing only violations, but can be increased if necessary. The final versions verdict is still calculated and printed at the end and the program exit code signifies whether the specified targets were met (0) or violated (1).

.. code-block:: console

% cat import argparse # 2.7, 3.2 all() # 2.5, 3.0 enumerate() # 2.3, 3.0

% ./ -t=2.4- -t=3 --violations ; echo $? Detecting python files.. Analyzing using 8 processes.. 2.7, 3.2 'all' member requires 2.5, 3.0 'argparse' module requires 2.7, 3.2

Minimum required versions: 2.7, 3.2 Target versions not met: 2.4-, 3.0 1

The two first lines violate the targets but the third line matches and is therefore not shown.

API (experimental)

Information such as minimum versions, used functionality constructs etc. can also be accessed programmatically via the vermin Python module, though it's an experimental feature. It is still recommended to use the command-line interface.

.. code-block:: python

import vermin as V V.version_strings(V.detect("a = long(1)")) '2.0, !3'

config = V.Config() config.add_exclusion("long") V.version_strings(V.detect("a = long(1)", config)) '~2, ~3'

config.set_verbose(3) v = V.visit("""from argparse import ArgumentParser ... ap = ArgumentParser(allow_abbrev=True) ... """, config) print(v.output_text(), end="") L1 C5: 'argparse' module requires 2.7, 3.2 L2: 'argparse.ArgumentParser(allow_abbrev)' requires !2, 3.5 V.version_strings(v.minimum_versions()) '!2, 3.5'

Lax Mode

Vermin parses Python source code into abstract syntax trees (ASTs) which it traverses to do analysis. However, it doesn't do conditional logic, i.e. deciding which branches will be taken at runtime, since it can cause unexpected side-effects to actually evaluate code. As an example, analysis of the following:

.. code-block:: python

if False: print(f"..but I won't be evaluated")

Will yield "f-strings require 3.6+" even though the branch will not be evaluated at runtime.

The lax mode, via argument --lax, was created to circumvent cases like this. But it's not a perfect solution since it will skip all if, ternarys, for, async for, while, with, try, and boolean operations. Therefore it is recommended to run with and without lax mode to get a better understanding of individual cases.

Analysis Exclusions

Another approach to conditional logic than lax mode, is to exclude modules, members, kwargs, codecs error handler names, or codecs encodings by name from being analysed via argument --exclude <name> (multiple can be specified). Consider the following code block that checks if PROTOCOL_TLS is an attribute of ssl:

.. code-block:: python

import ssl tls_version = ssl.PROTOCOL_TLSv1 if hasattr(ssl, "PROTOCOL_TLS"): tls_version = ssl.PROTOCOL_TLS

It will state that "'ssl.PROTOCOL_TLS' requires 2.7, 3.6" but to exclude that from the results, use --exclude 'ssl.PROTOCOL_TLS'. Afterwards, only "'ssl' requires 2.6, 3.0" will be shown and the final minimum required versions are v2.6 and v3.0 instead of v2.7 and v3.6.

Code can even be excluded on a more fine grained level using the # novermin or # novm comments at line level. The following yields the same behavior as the previous code block, but only for that particular if and its body:

.. code-block:: python

import ssl tls_version = ssl.PROTOCOL_TLSv1 if hasattr(ssl, "PROTOCOL_TLS"): # novermin tls_version = ssl.PROTOCOL_TLS

In scenarios where multiple tools are employed that use comments for various features, exclusions can be defined by having # for each comment "segment":

.. code-block:: python

if hasattr(ssl, "PROTOCOL_TLS"): # noqa # novermin # pylint: disable=no-member tls_version = ssl.PROTOCOL_TLS


Contributions are very welcome, especially adding and updating detection rules of modules, functions, classes etc. to cover as many Python versions as possible. For PRs, make sure to keep the code vanilla Python and run make test first. Note that code must remain valid and working on Python v2.7+ and v3+.

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