Fix accumulating memory issue

[Zain-Mahmoud]

Proposed Changes

This PR aims to fix the issue where repeated calls to the PyTA check_all() function cause the memory usage of the process to increase with each call (issue #646).

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Questions and Comments

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[Zain-Mahmoud]

Investigation

import io
import tracemalloc
import python_ta

def run_runner():
    buf = io.StringIO()
    python_ta.check_all(output=buf)

tracemalloc.start()

for i in range(5000):
    run_runner()
    current = tracemalloc.get_traced_memory()
    print(f"{i} | {int(current[0] / 1024**2)} MB")

Running the above code snippet, we can see that the memory usage does in fact increase with each call:

0 | 42 MB
1 | 44 MB
2 | 46 MB
3 | 48 MB
4 | 49 MB
5 | 51 MB
6 | 53 MB
7 | 55 MB
8 | 56 MB
9 | 58 MB
...
91 | 121 MB
92 | 122 MB
93 | 124 MB
94 | 125 MB
95 | 127 MB
96 | 128 MB
97 | 130 MB
98 | 132 MB
99 | 133 MB
...

But there does seem to be some freeing of memory (approximately 20 or so MB) every ~20 calls.

I also checked both Pylint and Astroid's changelogs but I couldn't find any fixes related to any memory leak issues.