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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 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 2974 rules, covering v2.0-2.7 and v3.0-3.8, divided into 134 modules, 2180 classes/functions/constants members of modules, 628 kwargs of functions, 4 strftime directives, 3 bytes format 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, coroutines (async and await), asynchronous generators (await and yield in same function), asynchronous comprehensions, await in comprehensions, boolean constants, named expressions, keyword-only parameters, 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, 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, and generalized unpacking. 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 3244 unit and integration tests employing 3869 assertions.

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

Or via 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


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.


% ./ -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

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


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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