Getopt overwrites variables unexpectedly

[jak]

BPO	24556
Nosy	@bitdancer

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2015-07-03.14:33:46.094>
created_at = <Date 2015-07-03.09:32:15.511>
labels = ['invalid', 'type-bug', 'library']
title = 'Getopt overwrites variables unexpectedly'
updated_at = <Date 2015-07-03.14:33:46.092>
user = 'https://bugs.python.org/Jak'

bugs.python.org fields:

activity = <Date 2015-07-03.14:33:46.092>
actor = 'r.david.murray'
assignee = 'none'
closed = True
closed_date = <Date 2015-07-03.14:33:46.094>
closer = 'r.david.murray'
components = ['Library (Lib)']
creation = <Date 2015-07-03.09:32:15.511>
creator = 'Jak'
dependencies = []
files = []
hgrepos = []
issue_num = 24556
keywords = []
message_count = 2.0
messages = ['246153', '246181']
nosy_count = 2.0
nosy_names = ['r.david.murray', 'Jak']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24556'
versions = ['Python 2.7', 'Python 3.4']

[jak]

The getopt library has, what I assume is, some unexpected behaviour when adding extra text to command line parameter that getopt expects as a flag.

Using input parameters a, b and c as an example below, where a and b both take values and c is a flag.

Example code:
options, remainders = getopt.getopt(sys.argv[1:], "a:b:c")

Normal output is given when you supply sensible values for a, b and c:

Input: -a value1 -b value2 -c
Output: [('-a', 'value1'), ('-b', 'value2'), ('-c', '')]

Unexpected output happens when you give extra text after the '-c' that begins with a letter matching that of a previous parameter:

Input -a value1 -b value2 -cbanana
Output: [('-a', 'value1'), ('-b', 'value2'), ('-c', ''), ('-b', 'anana')]

Looping through the output variables, as most example programs do, results in the value for '-b' being over-written.

[bitdancer]

This behavior is correct:

rdmurray@session:~>getopt a:b:c -a value1 -b value2 -cbanana
-a value1 -b value2 -c -b anana --