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About python : How-can-I-remove-the-ANSI-escape-sequences-from-a-string-in-python

Question Detail

Here is a snippet that includes my string.
'ls\r\n\x1b[00m\x1b[01;31mexamplefile.zip\x1b[00m\r\n\x1b[01;31m'

The string was returned from an SSH command that I executed. I can’t use the string in its current state because it contains ANSI standardized escape sequences. How can I programmatically remove the escape sequences so that the only part of the string remaining is 'examplefile.zip'.

Question Answer

Delete them with a regular expression:

import re

# 7-bit C1 ANSI sequences
ansi_escape = re.compile(r'''
    \x1B  # ESC
    (?:   # 7-bit C1 Fe (except CSI)
        [@-Z\\-_]
    |     # or [ for CSI, followed by a control sequence
        \[
        [0-?]*  # Parameter bytes
        [ -/]*  # Intermediate bytes
        [@-~]   # Final byte
    )
''', re.VERBOSE)
result = ansi_escape.sub('', sometext)

or, without the VERBOSE flag, in condensed form:

ansi_escape = re.compile(r'\x1B(?:[@-Z\\-_]|\[[0-?]*[ -/]*[@-~])')
result = ansi_escape.sub('', sometext)

Demo:

>>> import re
>>> ansi_escape = re.compile(r'\x1B(?:[@-Z\\-_]|\[[0-?]*[ -/]*[@-~])')
>>> sometext = 'ls\r\n\x1b[00m\x1b[01;31mexamplefile.zip\x1b[00m\r\n\x1b[01;31m'
>>> ansi_escape.sub('', sometext)
'ls\r\nexamplefile.zip\r\n'

The above regular expression covers all 7-bit ANSI C1 escape sequences, but not the 8-bit C1 escape sequence openers. The latter are never used in today’s UTF-8 world where the same range of bytes have a different meaning.

If you do need to cover the 8-bit codes too (and are then, presumably, working with bytes values) then the regular expression becomes a bytes pattern like this:

# 7-bit and 8-bit C1 ANSI sequences
ansi_escape_8bit = re.compile(br'''
    (?: # either 7-bit C1, two bytes, ESC Fe (omitting CSI)
        \x1B
        [@-Z\\-_]
    |   # or a single 8-bit byte Fe (omitting CSI)
        [\x80-\x9A\x9C-\x9F]
    |   # or CSI + control codes
        (?: # 7-bit CSI, ESC [ 
            \x1B\[
        |   # 8-bit CSI, 9B
            \x9B
        )
        [0-?]*  # Parameter bytes
        [ -/]*  # Intermediate bytes
        [@-~]   # Final byte
    )
''', re.VERBOSE)
result = ansi_escape_8bit.sub(b'', somebytesvalue)

which can be condensed down to

# 7-bit and 8-bit C1 ANSI sequences
ansi_escape_8bit = re.compile(
    br'(?:\x1B[@-Z\\-_]|[\x80-\x9A\x9C-\x9F]|(?:\x1B\[|\x9B)[0-?]*[ -/]*[@-~])'
)
result = ansi_escape_8bit.sub(b'', somebytesvalue)

For more information, see:

  • the ANSI escape codes overview on Wikipedia
  • ECMA-48 standard, 5th edition (especially sections 5.3 and 5.4)

The example you gave contains 4 CSI (Control Sequence Introducer) codes, as marked by the \x1B[ or ESC [ opening bytes, and each contains a SGR (Select Graphic Rendition) code, because they each end in m. The parameters (separated by ; semicolons) in between those tell your terminal what graphic rendition attributes to use. So for each \x1B[....m sequence, the 3 codes that are used are:

  • 0 (or 00 in this example): reset, disable all attributes
  • 1 (or 01 in the example): bold
  • 31: red (foreground)

However, there is more to ANSI than just CSI SGR codes. With CSI alone you can also control the cursor, clear lines or the whole display, or scroll (provided the terminal supports this of course). And beyond CSI, there are codes to select alternative fonts (SS2 and SS3), to send ‘private messages’ (think passwords), to communicate with the terminal (DCS), the OS (OSC), or the application itself (APC, a way for applications to piggy-back custom control codes on to the communication stream), and further codes to help define strings (SOS, Start of String, ST String Terminator) or to reset everything back to a base state (RIS). The above regexes cover all of these.

Note that the above regex only removes the ANSI C1 codes, however, and not any additional data that those codes may be marking up (such as the strings sent between an OSC opener and the terminating ST code). Removing those would require additional work outside the scope of this answer.

The accepted answer only takes into account ANSI Standardized escape sequences that are formatted to alter foreground colors & text style.
Many sequences do not end in 'm', such as: cursor positioning, erasing, and scroll regions. The pattern bellow attempts to cover all cases beyond setting foreground color and text-style.

Below is the regular expression for ANSI standardized control sequences:
/(\x9B|\x1B\[)[0-?]*[ -\/]*[@-~]/

Additional References:
  • ECMA-48 Section 5.4
  • ANSI escape code

Function

Based on Martijn Pieters♦’s answer with Jeff’s regexp.

def escape_ansi(line):
    ansi_escape = re.compile(r'(?:\x1B[@-_]|[\x80-\x9F])[0-?]*[ -/]*[@-~]')
    return ansi_escape.sub('', line)

Test

def test_remove_ansi_escape_sequence(self):
    line = '\t\u001b[0;35mBlabla\u001b[0m                                  \u001b[0;36m172.18.0.2\u001b[0m'

    escaped_line = escape_ansi(line)

    self.assertEqual(escaped_line, '\tBlabla                                  172.18.0.2')

Testing

If you want to run it by yourself, use python3 (better unicode support, blablabla). Here is how the test file should be:

import unittest
import re

def escape_ansi(line):
    …

class TestStringMethods(unittest.TestCase):
    def test_remove_ansi_escape_sequence(self):
    …

if __name__ == '__main__':
    unittest.main()

The suggested regex didn’t do the trick for me so I created one of my own.
The following is a python regex that I created based on the spec found here

ansi_regex = r'\x1b(' \
             r'(\[\??\d+[hl])|' \
             r'([=<>a-kzNM78])|' \
             r'([\(\)][a-b0-2])|' \
             r'(\[\d{0,2}[ma-dgkjqi])|' \
             r'(\[\d+;\d+[hfy]?)|' \
             r'(\[;?[hf])|' \
             r'(#[3-68])|' \
             r'([01356]n)|' \
             r'(O[mlnp-z]?)|' \
             r'(/Z)|' \
             r'(\d+)|' \
             r'(\[\?\d;\d0c)|' \
             r'(\d;\dR))'
ansi_escape = re.compile(ansi_regex, flags=re.IGNORECASE)

I tested my regex on the following snippet (basically a copy paste from the ascii-table.com page)

\x1b[20h    Set
\x1b[?1h    Set
\x1b[?3h    Set
\x1b[?4h    Set
\x1b[?5h    Set
\x1b[?6h    Set
\x1b[?7h    Set
\x1b[?8h    Set
\x1b[?9h    Set
\x1b[20l    Set
\x1b[?1l    Set
\x1b[?2l    Set
\x1b[?3l    Set
\x1b[?4l    Set
\x1b[?5l    Set
\x1b[?6l    Set
\x1b[?7l    Reset
\x1b[?8l    Reset
\x1b[?9l    Reset
\x1b=   Set
\x1b>   Set
\x1b(A  Set
\x1b)A  Set
\x1b(B  Set
\x1b)B  Set
\x1b(0  Set
\x1b)0  Set
\x1b(1  Set
\x1b)1  Set
\x1b(2  Set
\x1b)2  Set
\x1bN   Set
\x1bO   Set
\x1b[m  Turn
\x1b[0m Turn
\x1b[1m Turn
\x1b[2m Turn
\x1b[4m Turn
\x1b[5m Turn
\x1b[7m Turn
\x1b[8m Turn
\x1b[1;2    Set
\x1b[1A Move
\x1b[2B Move
\x1b[3C Move
\x1b[4D Move
\x1b[H  Move
\x1b[;H Move
\x1b[4;3H   Move
\x1b[f  Move
\x1b[;f Move
\x1b[1;2    Move
\x1bD   Move/scroll
\x1bM   Move/scroll
\x1bE   Move
\x1b7   Save
\x1b8   Restore
\x1bH   Set
\x1b[g  Clear
\x1b[0g Clear
\x1b[3g Clear
\x1b#3  Double-height
\x1b#4  Double-height
\x1b#5  Single
\x1b#6  Double
\x1b[K  Clear
\x1b[0K Clear
\x1b[1K Clear
\x1b[2K Clear
\x1b[J  Clear
\x1b[0J Clear
\x1b[1J Clear
\x1b[2J Clear
\x1b5n  Device
\x1b0n  Response:
\x1b3n  Response:
\x1b6n  Get
\x1b*[ -/]*[@-~]')
    return ansi_escape.sub('', str(line))

none of the regex solutions worked in my case with OSC sequences (\x1b])

to actually render the visible output, you will need a terminal emulator like pyte

#! /usr/bin/env python3

import pyte # terminal emulator: render terminal output to visible characters

pyte_screen = pyte.Screen(80, 24)
pyte_stream = pyte.ByteStream(pyte_screen)

bytes_ = b''.join([
  b'$ cowsay hello\r\n', b'\x1b[?2004l', b'\r', b' _______\r\n',
  b'< hello >\r\n', b' -------\r\n', b'        \\   ^__^\r\n',
  b'         \\  (oo)\\_______\r\n', b'            (__)\\       )\\/\\\r\n',
  b'                ||----w |\r\n', b'                ||     ||\r\n',
  b'\x1b]0;[email protected]:/tmp\x1b\\', b'\x1b]7;file://laptop1/tmp\x1b\\', b'\x1b[?2004h$ ',
])
pyte_stream.feed(bytes_)

# pyte_screen.display always has 80x24 characters, padded with whitespace
# -> use rstrip to remove trailing whitespace from all lines
text = ("".join([line.rstrip() + "\n" for line in pyte_screen.display])).strip() + "\n"
print("text", text)

print("cursor", pyte_screen.cursor.y, pyte_screen.cursor.x)
print("title", pyte_screen.title)

if you want to remove the \r\n bit, you can pass the string through this function (written by sarnold):

def stripEscape(string):
    """ Removes all escape sequences from the input string """
    delete = ""
    i=1
    while (i<0x20):
        delete += chr(i)
        i += 1
    t = string.translate(None, delete)
    return t

Careful though, this will lump together the text in front and behind the escape sequences. So, using Martijn’s filtered string 'ls\r\nexamplefile.zip\r\n', you will get lsexamplefile.zip. Note the ls in front of the desired filename.

I would use the stripEscape function first to remove the escape sequences, then pass the output to Martijn’s regular expression, which would avoid concatenating the unwanted bit.

For 2020 with python 3.5 it as easy as string.encode().decode('ascii')

ascii_string = 'ls\r\n\x1b[00m\x1b[01;31mexamplefile.zip\x1b[00m\r\n\x1b[01;31m'
decoded_string = ascii_string.encode().decode('ascii')
print(decoded_string) 

>ls
>examplefile.zip
>

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