python3 replacing double backslash with single bac

问题:

This question already has an answer here:

• Python Replace \\ with \ 6 answers

I need to replace \\ with \ in python3 in a complex string. I know that this question had been asked several times, but most of the time for simple strings so that none of the (accepted) answers really works for complex strings.

This is also different from this one where the problem could be solved with .decode('unicode_escape') which does not work for this problem. See below.

Assuming the string is:

my_str = '\\xa5\\xc0\\xe6aK\\xf9\\x80\\xb1\\xc8*\x01\x12$\\xfbp\x1e(4\\xd6{;Z\\x'

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Straight forward approach would be:

my_str.replace('\\','\')

which leads to:

SyntaxError: EOL while scanning string literal

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This answer suggests using:

my_str.replace('\\\\','\\')

Which results in:

'\\xa5\\xc0\\xe6aK\\xf9\\x80\\xb1\\xc8*\x01\x12$\\xfbp\x1e(4\\xd6{;Z\\x'

So, there is no change.

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This answer suggests:

b = bytes(my_str, encoding='utf-8')
b.decode('unicode-escape')

But this doesn't work for such a complex string:

UnicodeDecodeError: 'unicodeescape' codec can't decode bytes in position 49-50: truncated \xXX escape

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Using decode (as suggested here) results in:

my_str.decode('unicode_escape')

AttributeError: 'my_str' object has no attribute 'decode'

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A combination of encoding and then decoding using unicode_esacpe returns a totally different string (probably due to using utf-16, but utf-8 results in an error, see above. Also, e.g. latin1 doesn't work):

my_str.encode('utf-16').decode('unicode_escape')
'ÿþ\\\x00x\x00a\x005\x00\\\x00x\x00c\x000\x00\\\x00x\x00e\x006\x00a\x00K\x00\\\x00x\x00f\x009\x00\\\x00x\x008\x000\x00\\\x00x\x00b\x001\x00\\\x00x\x00c\x008\x00*\x00\x01\x00\x12\x00$\x00\\\x00x\x00f\x00b\x00p\x00\x1e\x00(\x004\x00\\\x00x\x00d\x006\x00{\x00;\x00Z\x00\\\x00x\x00'

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回答1:

Take a closer look at the string, they are all single slash.

In [26]: my_str[0]
Out[26]: '\\'

In [27]: my_str[1]
Out[27]: 'x'

In [28]: len(my_str[0])
Out[28]: 1

And my_str.replace('\\','\') won't work because the token here is \', which escapes ' and waits for the another closing '.
Use my_str.replace('\\', '') instead

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Update: after few more days, I realize the following discussion may also be helpful. If the intension of a string with escape ('\\x' or '\\u') are eventually hex/unicode literals, they can be decoded by escape_decode.

import codecs
print(len(b'\x32'), b'\x32')                # 1 hex literal, '\x32' == '2'
print(len(b'\\x32'), b'\\x32')              # 4 chars including escapes
print(codecs.escape_decode('\\x32', 'hex')) # chars->literal, 4->1

# 1 b'2'
# 4 b'\\x32'
# (b'2', 4)

s = '\\xa5\\xc0\\xe6aK\\xf9\\x80\\xb1\\xc8*\x01\x12$\\xfbp\x1e(4\\xd6{;Z'
ed, _ = codecs.escape_decode(s, 'hex')
print(len(s), s)
print(len(ed), ed)

# 49 \xa5\xc0\xe6aK\xf9\x80\xb1\xc8*$\xfbp(4\xd6{;Z
# 22 b'\xa5\xc0\xe6aK\xf9\x80\xb1\xc8*\x01\x12$\xfbp\x1e(4\xd6{;Z'

回答2:

If you do

s  = '\\xa5\\xc0\\xe6aK\\xf9\\x80\\xb1\\xc8*\x01\x12$\\xfbp\x1e(4\\xd6{;Z\\x'

s = s.replace('\\','\')

print(s)

you get

 File "main.py", line 3
    s = s.replace('\\','\')
                         ^
SyntaxError: EOL while scanning string literal

because in '\' the \ escapes the ' . Your string is left open.

You do not have any double \ in s - its just displaying it as such, do distinguish it from \ used to escape stuff if you inspect it.

If you print(s) you get \xa5\xc0\xe6aK\xf9\x80\xb1\xc8*$\xfbp(4\xd6{;Z\x