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Python Big-O: Time & Space Complexity

Compileall

compileall Module¶

The compileall module compiles all Python source files in a directory tree to bytecode (.pyc files).

Complexity Reference¶

Operation	Time	Space	Notes
`compile_dir()`	O(E + B)	O(E + M)	E = every directory entry examined, not just `.py` files; B = source bytes compiled; M = the largest single file's compilation working set, which dominates. Measured on CPython 3.11, one Linux machine, tmpfs - illustrative: 5000 non-Python files added to 20 modules made it 10.9x slower, 200 ten-line files cost about nine times 10 two-hundred-line files, and one 1.8 MB module peaked at 232 MB
`compile_file()`	O(m)	O(m)	m = file size; one file
`workers=N`	-	O(E + N*M)	Each process holds its own copy of M, so peak memory scales with the worker count
`compile_path()`	O(E + B)	O(E + M)	Same walk, over the entries of each `sys.path` directory
`main()`	O(E + B)	O(E + M)	CLI entrypoint

Batch Compiling Python Files¶

Compile Directory¶

import compileall
import tempfile
from pathlib import Path

tree = Path(tempfile.mkdtemp())
(tree / 'example.py').write_text('value = 1\n')

# Compile directory tree - O(E + B)
compileall.compile_dir(tree)

# With options
compileall.compile_dir(
    tree,
    force=True,        # Recompile all
    quiet=0            # Show progress
)

# workers=N compiles files in parallel (workers=0 uses one per CPU)
compileall.compile_dir(tree, workers=4, quiet=1)

# Or from command line:
# python -m compileall /path/to/code

The return value only reports compilation failures

compile_dir() returns False when a file fails to compile, and True otherwise - including when it could not read the directory at all. A path that does not exist, or that is a file rather than a directory, is reported as success.

import compileall
import tempfile
from pathlib import Path

tree = Path(tempfile.mkdtemp())
(tree / 'broken.py').write_text('def (\n')

compileall.compile_dir(tree, quiet=2)               # False - a real failure
compileall.compile_dir(tree / 'nowhere', quiet=2)   # True, despite listing nothing
compileall.compile_dir(tree / 'broken.py', quiet=2)  # True, and it is not a directory

# So check the path yourself before trusting the result
def compile_tree(path):
    if not path.is_dir():
        raise NotADirectoryError(path)
    return compileall.compile_dir(path, quiet=2)

print(compile_tree(tree))  # False - broken.py is still in there

Compile Single File¶

import py_compile
import tempfile
from pathlib import Path

source = Path(tempfile.mkdtemp()) / 'myfile.py'
source.write_text('value = 1\n')

# Compile one file - O(m) in the file's size
py_compile.compile(source)

# A missing file raises rather than returning None - doraise only controls
# what happens to compilation errors, not to reading the source
try:
    py_compile.compile(source.with_name('absent.py'))
except FileNotFoundError as error:
    print(f'no such source: {error.filename}')