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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 can be run with v3+ but still includes detection of v2.x functionality.

It functions by parsing Python code into an abstract syntax tree (AST), which it traverses and matches against internal dictionaries with 3796 rules, covering v2.0-2.7 and v3.0-3.12, divided into 178 modules, 2614 classes/functions/constants members of modules, 875 kwargs of functions, 4 strftime directives, 3 bytes format directives, 2 array typecodes, 3 codecs error handler names, 20 codecs encodings, 78 builtin generic annotation types, 9 builtin dict union (|) types, 8 builtin dict union merge (|=) types, and 2 user function decorators.

Backports of the standard library, like typing, can be enabled for better results. Get full list of backports via --help.

The project is fairly well-tested with 4008 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.

Table of Contents


It is fairly straightforward to use Vermin.

Running it from the repository either directly or through specific interpreter:

% ./ /path/to/your/project        # (1) executing via `/usr/bin/env python`
% python3 /path/to/your/project  # (2) specifically `python3`

Or if installed via PyPi:

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

Homebrew (pkg):

% brew install vermin

Spack (pkg):

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

Arch Linux (AUR):

% yay -S python-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
- vermin -t=2.7 -t=3 project_package

Vermin can also be used as a pre-commit hook:

  - repo:
    rev: GIT_SHA_OR_TAG  # ex: 'e88bda9' or 'v1.3.4'
      - id: vermin
        # specify your target version here, OR in a Vermin config file as usual:
        args: ['-t=3.8-', '--violations']
        # (if your target is specified in a Vermin config, you may omit the 'args' entry entirely)

When using the hook, a target version must be specified via a Vermin config file in your package, or via the args option in your .pre-commit-config.yaml config. If you're passing the target via args, it's recommended to also include --violations (shown above).

If you're using the vermin-all hook, you can specify any target as you usually would. However, if you're using the vermin hook, your target must be in the form of x.y- (as opposed to x.y), otherwise you will run into issues when your staged changes meet a minimum version that is lower than your target.

See the pre-commit docs for further general information on how to get hooks set up on your project.


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 ..), except*, 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, asynchronous with statement, multiple context expressions in a with statement, multiple context expressions in a with statement grouped with parenthesis, 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, relaxed decorators, metaclass class keyword, pattern matching with match, union types written as X | Y, and type alias statements (type X = SomeType). It tries to detect and ignore user-defined functions, classes, arguments, and variables with names that clash with library-defined symbols.


For frequently asked questions, check out the FAQ discussions.

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.

Detecting union types (X | Y PEP 604) can be tricky because Vermin doesn't know all underlying details of constants and types since it parses and traverses the AST. For this reason, heuristics are employed and this can sometimes yield incorrect results (#103). To enable (unstable) union types detection, use --feature union-types.

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, .p4root, .pijul

A sample config file can be found here.

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

verbose = 1
processes = 4

ignore = E111,F821


% ./ vermin
Minimum required versions: 3.0
Incompatible versions:     2

% ./ -t=3.3 vermin
Minimum required versions: 3.0
Incompatible versions:     2
Target versions not met:   3.3
% echo $?

% ./ --versions vermin
Minimum required versions: 3.0
Incompatible versions:     2
Version range:             2.0, 2.6, 2.7, 3.0

% ./ -v examples
Detecting python files..
Analyzing 6 files using 8 processes..
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/
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

See Parsable Output for more information about parsable output format.

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 (or --lint) 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). However, if no rules are triggered the exit code will be 0 due to inconclusivity.

% 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

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.

>>> 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'

Analysis Exclusions

Analysis exclusion can be necessary in certain cases. The argument --exclude <name> (multiple can be specified) can be used to exclude modules, members, kwargs, codecs error handler names, or codecs encodings by name from being analysed via . Consider the following code block that checks if PROTOCOL_TLS is an attribute of ssl:

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:

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":

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

Note that if a code base does not have any occurrences of # novermin or # novm, speedups up to 30-40%+ can be achieved by using the --no-parse-comments argument or parse_comments = no config setting.

Parsable Output

For scenarios where the results of Vermin output is required, it is recommended to use the parsable output format (--format parsable) instead of the default output. With this format enabled, each line will be on the form:


The <line> and <column> are only shown when the verbosity level is high enough, otherwise they are empty.

Each feature detected per processed file will have the <feature> defined on an individual line. The last line of the processed file will have a special line with the corresponding <file> and no <feature>, constituting the minimum versions of that file:


The very last line is the final minimum versions results of the entire scan and therefore has no <file> and <feature>:


Inspection of example output

% ./ -f parsable /path/to/project
/path/to/project/'abc' module
/path/to/project/!2:3.4:'abc.ABC' member
:::!2:3.4: requires !2 and 3.4 via:

/path/to/project/!2:3.4: requires ~2 and ~3 via:


And requires !2 and 3.0 via:


That means that the final result is !2 and 3.4, which is shown by the last line:



Contributions are very welcome, especially adding and updating detection rules of modules, functions, classes etc. to cover as many Python versions as possible. See for more information.