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Lib/getopt.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/getopt.py

getopt provides traditional Unix option parsing. It is considered lower-level than argparse; most new code should use argparse. getopt is still widely used in scripts and tools that want minimal dependencies or exact POSIX option compatibility.

Map​

LinesSymbolRole
1-40GetoptError, errorException class
41-120getoptPOSIX-style option parsing
121-210gnu_getoptGNU-style parsing allowing options after non-option args

Reading​

getopt​

getopt(args, shortopts, longopts=[]) parses args against a short option string and a list of long option names.

# CPython: Lib/getopt.py:52 getopt
def getopt(args, shortopts, longopts=[]):
    opts = []
    if type(longopts) == type(""):
        longopts = [longopts]
    else:
        longopts = list(longopts)
    while args and args[0].startswith('-') and args[0] != '-':
        if args[0].startswith('--'):
            opts, args = do_longs(opts, args[0][2:], longopts, args[1:])
        else:
            opts, args = do_shorts(opts, args[0][1:], shortopts, args[1:])
    return opts, args

Short options: a string like 'hvo:' where : means the option takes an argument. Long options: a list like ['help', 'verbose', 'output='] where = means the option takes an argument.

Returns (opts, args): opts is a list of (option, value) pairs; args is the remaining non-option arguments.

gnu_getopt​

Like getopt but continues parsing after the first non-option argument instead of stopping. This matches GNU convention where cmd arg1 -v arg2 is valid.

# CPython: Lib/getopt.py:126 gnu_getopt
def gnu_getopt(args, shortopts, longopts=[]):
    opts = []
    prog_args = []
    ...
    while args:
        if args[0].startswith('--') and len(args[0]) > 2:
            opts, args = do_longs(opts, args[0][2:], longopts, args[1:])
        elif args[0].startswith('-') and args[0] != '-':
            opts, args = do_shorts(opts, args[0][1:], shortopts, args[1:])
        else:
            if all_options_first:
                prog_args += args
                break
            prog_args.append(args[0])
            args = args[1:]
    return opts, prog_args

gopy notes​

Status: not yet ported. Pure Python, very small. Direct Go port of the two functions with a GetoptError equivalent. No special CPython internals needed.