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jbranchaud
39 lines
1.3 KiB
Markdown
39 lines
1.3 KiB
Markdown
# Assert Is Only A Development Check
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The `assert` keyword is used in Python to write a statement that will check some
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assertion and raise an error if it isn't met. This is only meant to be used as a
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check during development because it can be easily optimized out of the code.
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```python
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stuff = None
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assert stuff, "We need to have some stuff to proceed"
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print(f"We have {stuff or 'something'}!")
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```
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If I execute this code with `python`, it will raise on that second line of code.
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```bash
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❯ python assert_example.py
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Traceback (most recent call last):
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File "/Users/lastword/dev/jbranchaud/py-vmt/assert_example.py", line 3, in <module>
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assert stuff, "We need to have some stuff to proceed"
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^^^^^
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AssertionError: We need to have some stuff to proceed
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```
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This `assert` statement will be stripped out of the compiled bytecode if the
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`-O` (capital o) flag is used. Notice how running the same file with that flag
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does not lead to an `AssertionError`.
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```python
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❯ python -O assert_example.py
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We have something!
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```
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If I want to make sanity checks for situations that would be caused by a bug in
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the code, an `assert` statement can be a good candidate. However, if I am making
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runtime checks like validating user input, then an `if` statement and raising
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something like a `ValueError` is better.
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