CodeQL documentation

Should use a ‘with’ statement

ID: py/should-use-with
Kind: problem
Severity: recommendation
Precision: very-high
Tags:
   - maintainability
   - readability
   - convention
Query suites:
   - python-security-and-quality.qls

Click to see the query in the CodeQL repository

The with statement was introduced by PEP343 to allow standard uses of try-finally statements to be factored out. Using this simplification makes code easier to read.

Recommendation

Review the code and determine whether or not the try-finally is used only to ensure that a resource is closed. If the only purpose is to ensure that a resource is closed, then replace the try-finally statement with a with statement.

Example

The following code shows examples of different ways of ensuring that a file is always closed, even when an error is generated. In the second example, the try-finally block is replaced by a simpler with statement.


f = open("filename")
try:                         # Method of ensuring file closure
    f.write(...)
finally:
    f.close()


with open("filename") as f:  # Simpler method of ensuring file closure
    f.write(...)

References