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errno Module¶

The errno module provides platform-specific error number constants and an errorcode mapping for converting between numeric error codes and their symbolic names.

Complexity Reference¶

Operation	Time	Space	Notes
Access `E*` constant	O(1)	O(1)	Integer constant lookup
`errorcode[err]`	O(1)	O(1)	Dict lookup for symbolic name
Compare `exc.errno`	O(1)	O(1)	Integer compare

Platform-dependent constants

errno values are OS-dependent. Some constants may be missing or have different numeric values across platforms.

Common Operations¶

Check an `OSError` by errno¶

import errno

try:
    with open("missing.txt", "r") as handle:
        data = handle.read()
except OSError as exc:
    if exc.errno == errno.ENOENT:
        print("File not found")
    elif exc.errno == errno.EACCES:
        print("Permission denied")
    else:
        raise

Map an error code to its name¶

import errno

# O(1) lookup
name = errno.errorcode[errno.ENOENT]  # "ENOENT"

Use errno in filesystem helpers¶

import errno
import os

try:
    os.remove("tmp.txt")
except FileNotFoundError as exc:
    # FileNotFoundError derives from OSError
    if exc.errno == errno.ENOENT:
        pass

Public Constants¶

The module exposes many E* integer constants such as:

EACCES, EEXIST, EINVAL, EIO, ENOENT, ENOSPC, ENOTDIR, EPIPE
Socket-related errors like ECONNRESET, ECONNREFUSED, ETIMEDOUT

Use dir(errno) to list all constants available on your platform.