python.lang.correctness.writing-to-file-in-read-mode.writing-to-file-in-read-mode

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The file object '$FD' was opened in read mode, but is being written to. This will cause a runtime error.

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Defintion

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rules:
  - id: writing-to-file-in-read-mode
    message: The file object '$FD' was opened in read mode, but is being written to.
      This will cause a runtime error.
    patterns:
      - pattern-either:
          - pattern-inside: |
              $FD = open($NAME, "r", ...)
              ...
          - pattern-inside: |
              $FD = open($NAME, "rb", ...)
              ...
          - pattern-inside: |
              with open($NAME, "r", ...) as $FD:
                ...
          - pattern-inside: |
              with open($NAME, "rb", ...) as $FD:
                ...
      - pattern: $FD.write(...)
    severity: ERROR
    languages:
      - python
    metadata:
      category: correctness
      technology:
        - python
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]

Examples

writing-to-file-in-read-mode.py

fout = open("example.txt", 'w')
print("stuff")
# ok:writing-to-file-in-read-mode
fout.write("I'm writable!")
fout.close()


fout = open("example.txt", 'r')
print("stuff")
# ruleid:writing-to-file-in-read-mode
fout.write("whoops, I'm not writable!")
fout.close()


with open("example.txt", 'rb') as fout:
    # ruleid:writing-to-file-in-read-mode
    fout.write("whoops, me neither!")