idlelib Module Complexity¶

The idlelib package implements IDLE, Python's editor and shell. Its public surface is starting the application: python -m idlelib and the idle launcher scripts. Everything else in the package - the editor, the shell, syntax colouring, the debugger - is private implementation that can change in a bugfix release (PEP 434), so this page does not price it.

IDLE is a Tk application and needs a display. By default it also starts a second Python process to run user code, and talks to it over a local socket. f is the files named on the command line, s is the characters in them in total, and i is the characters read from standard input. Tk, the window system, the user-code process, and the code that -c or -r runs are not priced.

Complexity Reference¶

Starting IDLE¶

Operation	Time	Space	Notes
`import idlelib`	O(1)	O(1)	Defines one flag, `idlelib.testing`; imports no submodule and not `tkinter`
`python -m idlelib [options] [file ...]`	O(f² + s)	O(f + s)	At most one editor window per file, each file read whole into its window. Each file's directory joins `sys.path` unless already there, so files in f different directories cost O(f²). Needs a display: on Linux without one it exits with `TclError`
`python -m idlelib -`	O(i)	O(i)	Reads standard input to its end before creating any window, then runs it in the shell
`python -m idlelib -h`	O(1)	O(1)	Prints the usage and exits before creating any window, so it runs without a display

Importing the Package¶

import idlelib runs a package __init__ that sets one flag. The modules that make up IDLE load only when something imports them, which python -m idlelib does.

import subprocess
import sys

code = 'import sys, idlelib; print(sorted(m for m in sys.modules if "idlelib" in m or "tk" in m))'
result = subprocess.run([sys.executable, '-c', code], capture_output=True, text=True, check=True)
assert result.stdout == "['idlelib']\n"  # O(1) - no submodule, no tkinter

Starting IDLE Without a Window¶

-h is handled while the command line is parsed, before Tk is asked for a window, so it works on a machine with no display.

import subprocess
import sys

result = subprocess.run(
    [sys.executable, '-m', 'idlelib', '-h'], capture_output=True, text=True, check=True
)  # O(1) - prints the usage and exits
assert 'USAGE: idle' in result.stdout

Performance Best Practices¶

✅ Do:

Import idlelib freely; nothing loads until a submodule is imported

❌ Avoid:

Starting IDLE on a machine without a display; it fails once Tk is asked for a window
Building on idlelib submodules; they are private and their cost can change in a bugfix release

tkinter - the GUI toolkit IDLE is built on
code - the interactive interpreter classes IDLE's shell builds on