Color prompt + readline

[atagar1]

BPO	12972
Nosy	@terryjreedy

^{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 2011-09-18.17:10:26.040>
created_at = <Date 2011-09-13.15:29:32.097>
labels = ['type-bug']
title = 'Color prompt + readline'
updated_at = <Date 2014-05-25.21:45:07.984>
user = 'https://bugs.python.org/atagar1'

bugs.python.org fields:

activity = <Date 2014-05-25.21:45:07.984>
actor = 'terry.reedy'
assignee = 'none'
closed = True
closed_date = <Date 2011-09-18.17:10:26.040>
closer = 'terry.reedy'
components = []
creation = <Date 2011-09-13.15:29:32.097>
creator = 'atagar1'
dependencies = []
files = []
hgrepos = []
issue_num = 12972
keywords = []
message_count = 6.0
messages = ['143977', '144150', '144227', '144245', '219101', '219106']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'atagar', 'atagar1']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'test needed'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue12972'
versions = ['Python 2.7']

[atagar1]

Hi, when using terminal coloring codes (for instance '\x1b[32mhello world\x1b[0m' for a green 'hello world') the raw_input function and readline module behave well except under a very specific use case...

========================================

import readline # provides history via up/down

prompt = '\x1b[32m>>> \x1b[0m' # green '>>> ' prompt

while True:
  raw_input(prompt)

========================================

This provides a green prompt and up/down cycles through prior input. This works well as long as the input is shorter than the prompt string length (in this case 13 characters). However, if the input is longer than the prompt then up/down thinks that the first thirteen rendered characters now belong to the prompt. For instance...

atagar@fenrir:~/Desktop/arm$ python tmp.py 
>>> http://docs.python.org/library/readline

Press up, then down to get back to a blank prompt. You'll have...
>>> http://do

This is probably due to a len() check on the raw_input argument...
>>> len('>>> http://do')
13
>>> len('\x1b[32m>>> \x1b[0m')
13

I'm at a bit of a loss for investigating this further - help would be appreciated! -Damian

[terryjreedy]

From your version choice, you apparently are using 2.6, which is in security-fix only mode. Please test with the latest 2.7 and/or 3.2.

[atagar]

Retested with Python 3.1.1 and this issue doesn't manifest. This can be resolved - sorry about the noise. :)

[terryjreedy]

Since 2.7 was released after 3.1, I will assumed any bugfix was applied there also until someone determines otherwise. Thanks for checking.

[atagar]

Just a quick comment that I ran into this again, but turns out that it's not an issue with python. Rather, this is a quirk with how readline works...

https://stackoverflow.com/questions/9468435/look-how-to-fix-column-calculation-in-python-readline-if-use-color-prompt

Color prompts need to be wrapped by RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE.

[terryjreedy]

Thanks for the followup. This should be useful info for anyone who finds this issue.