Does Python's Integer Cache Impact Compiled Code's Integer Comparisons?

Does Python's Integer Cache Extend to Compiled Code?

While Python maintains an integer cache for values between -5 and 256, this cache does not directly affect integer comparisons in compiled code.

In compiled code, the compiler analyzes literals together, merging equal constant values into a single object to optimize memory usage. This behavior applies not only to integers but also to floats.

Example: Interactive vs. Compiled Code

Consider the following examples:

# Interactive
>>> a = 257
>>> b = 257
>>> a is b
False

In the interactive interpreter, each line is parsed and compiled separately. Thus, a and b refer to distinct PyInt_Objects despite their equivalent value.

# Compiled
$ echo 'a = 257
> b = 257
> print a is b' > test.py
$ python test.py
True

When compiling code from a file, the compiler analyzes the entire code and can merge identical literals. This means that a and b in this example will point to the same PyInt_Object, resulting in True for the is comparison.

Internal Optimization Details

The compiler's optimization process is performed by the compiler_add_o function, which uses a dictionary to store constants. Identical constants will occupy the same slot in the dictionary, leading to a single constant object in the compiled bytecode.

Exceptions to the Rule

The compiler's merging behavior does not apply to complex literals like tuples or lists. While the contained elements may be merged, the literals themselves will remain distinct objects.

>>> a = (257, 258)
>>> b = (257, 258)
>>> a is b
False
>>> a[0] is b[0]
True

Conclusion

Python's compiler performs significant optimizations to reduce memory usage, including merging identical constants in compiled code. While the integer cache itself does not directly impact these optimizations, integer comparisons involving identical values will still behave as expected, with equal values resulting in True for is and == comparisons.

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