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Concurrently detect the minimum Python versions needed to run code

Project description

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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 1207 rules, covering v2.0-2.7 and v3.0-3.8, divided into 132 modules, 853 classes/functions/constants members of modules, 193 kwargs of functions, 4 strftime directives, 2 array typecodes, 3 codecs error handler names, and 20 codecs encodings. Including looking for v2/v3 print expr and print(expr), long, f-strings, self-documenting f-strings, coroutines (async and await), asynchronous generators (await and yield in same function), asynchronous comprehensions, await in comprehensions, boolean constants, named expressions, positional-only parameters, yield from, exception context cause (raise .. from ..), 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, and function, function and variable annotations, continue in finally block, modular inverse pow(), array typecodes, codecs error handler names and encodings. It tries to detect and ignore user-defined functions, classes, arguments, and variables with names that clash with library-defined symbols.

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

The project is fairly well-tested with 1327 unit and integration tests.


It is fairly straightforward to use Vermin:

./ /path/to/your/project

Or via PyPi:

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

Or via Arch Linux (AUR):

% yay -S 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 0.9.0
Usage: ./ [options] <python source files and folders..>

Heuristics are employed when files don't have extensions 'py' or 'pyw':
  - Magic lines with 'python' are accepted, like: #!/usr/bin/env python
  - 'pyc' are ignored
  - Files that cannot be opened for reading as text devices are ignored

However, files directly specified are always attempted parsing, even without
accepted extensions or heuristics.

  -q    Quiet mode. It only prints the final versions verdict.
  -v..  Verbosity level 1 to 4. -v, -vv, -vvv, and -vvvv shows increasingly more
        -v     will show the individual versions required per file.
        -vv    will also show which modules, functions etc. that constitutes
               the requirements.
        -vvv   will also show line/col numbers.
        -vvvv  will also show user-defined symbols being ignored.
  -t=V  Target version that files must abide by. Can be specified once or twice.
        A '-' can be appended to match target version or smaller, like '-t=3.5-'.
        If not met Vermin will exit with code 1. Note that the amount of target
        versions must match the amount of minimum required versions detected.
  -p=N  Use N concurrent processes to analyze files (defaults to all cores = 8).
  -i    Ignore incompatible versions and warnings. However, if no compatible versions
        are found then incompatible versions will be shown in the end to not have an
        absence of results.
  -l    Lax mode: ignores conditionals (if, ternary, for, while, try, bool op) on AST
        traversal, which can be useful when minimum versions are detected in
        conditionals that it is known does not affect the results.
  -d    Dump AST node visits.

  --help | -h
        Shows this information.

        Analyze 'hidden' files and folders starting with '.' (ignored by default when not
        specified directly).

        In the end, print all unique versions required by the analysed code.

        Don't show any helpful tips at the end, like those relating to backports or
        lax mode.

  [--exclude <name>] ...
        Exclude full names, like 'email.parser.FeedParser', from analysis. Useful to
        ignore conditional logic that can trigger incompatible results. It's more fine
        grained than lax mode.

          Exclude '' module/member: --exclude ''
          Exclude 'foo' kwarg:                 --exclude 'somemodule.func(foo)'
          Exclude 'bar' codecs error handler:  --exclude 'ceh=bar'
          Exclude 'baz' codecs encoding:       --exclude 'ce=baz'

  [--exclude-file <file name>] ...
        Exclude full names like --exclude but from a specified file instead. Each line
        constitutes an exclusion with the same format as with --exclude.

  [--backport <name>] ...
        Some features are sometimes backported into packages, in repositories such as
        PyPi, that are widely used but aren't in the standard language. If such a
        backport is specified as being used, the results will reflect that instead.

        Supported backports:
          argparse     -
          configparser -
          enum         -
          faulthandler -
          typing       -

Results interpretation:
  ~2       No known reason it won't work with py2.
  !2       It is known that it won't work with py2.
  2.5, !3  Works with 2.5+ but it is known it won't work with py3.
  ~2, 3.4  No known reason it won't work with py2, works with 3.4+

% ./ -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 $?

% ./ -q --versions vermin
Minimum required versions: 2.7, 3.0
Version range:             2.0, 2.2, 2.5, 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 (None, 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 (None, 3.4)

Minimum required versions: 3.4
Incompatible versions:     2

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:

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 -l, was created to circumvent cases like this. But it’s not a perfect solution since it will skip all if, ternarys, for, while, 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:

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


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 be remain valid and working on Python v2.7+ and v3+.

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