Convert from string to tuple with "\" in python

Question

I transport data from command line to python. And I want to convert from string (command line) to tuple (python). But I have problem with \ charactor.

In command line, I using:

C:\>python music.py -a variable="?=="

In python:

#convert variable to array 
variable_array = variable.split("==")
#convert to tuple
variable_tuple = tuple(variable_array)

I get variable_tuple = ("?","")

The result what I need is variable_tuple = ("\?","")

When using

C:\>python music.py -a variable="\?=="

The result is variable_tuple = ("\\?","")

How can I transport data from command line to get tuple ("\?","") in python? I need backslash for "?"

Try `print '\\?'` in a prompt; it is *already* giving you what you want, but since a python literal uses `\` as an escape character it is escaping the escape character to make it a valid string literal. — Martijn Pieters, Jan 06 '13 at 12:44
There's no problem here: `assert variable_tuple == (r"\?", "")` — Eric, Jan 06 '13 at 14:15

score 4 · Accepted Answer · edited May 23 '17 at 11:59

4

'\\?' is a string with one backslash character and a question mark. Using list is a convenient trick for spliting a string into characters. For example:

In [34]: list('\\?')
Out[34]: ['\\', '?']

shows '\\?' is composed of 2 characters, not 3. And if you print it:

In [35]: print('\\')
\

you see it prints as just one backslash character. The double backslash, '\\', is an escape sequence.

Note also that when you print a tuple, you get the repr of its contents:

In [36]: print(tuple('\\?'))
('\\', '?')

'\?' is the exact same string as '\\?' in Python. They are simply different ways of representing the same string:

In [38]: list('\?')
Out[38]: ['\\', '?']

In [39]: list('\\?')
Out[39]: ['\\', '?']    

In [42]: '\?' is '\\?'
Out[44]: True

edited May 23 '17 at 11:59

Community

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answered Jan 06 '13 at 12:43

unutbu

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If input is "\\?", we will get ("\\\\?") – hoangvu68 Jan 06 '13 at 12:49
@hoangvu68: I don't have Windows to check, but yes, I believe so. – unutbu Jan 06 '13 at 12:54
@unutbu: I need backslash for "?" ("\?"). I don't want to add backslash before "\". – hoangvu68 Jan 06 '13 at 13:01
You need to make a clear distinction between the way strings are represented, eg `'\\?'`, and the way they are printed, e.g. `\?`. If you want a **single** backslash followed by a question mark, then the way that string is **represented** in Python is `'\\?'`. – unutbu Jan 06 '13 at 13:07
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Python chooses to represent this string as `'\\?'` even though `'\?'` represents the same string. You won't be able to change the way Python behaves in this respect without hacking the source code and recompiling Python. – unutbu Jan 06 '13 at 13:11
@unutbu: Thank you. I resloved it :) – hoangvu68 Jan 06 '13 at 14:13

score 0 · Answer 2 · answered Jan 06 '13 at 12:43

0

You get exactly what you want. What you see is just the string represenation for '\' with the first '\' as escape character.

answered Jan 06 '13 at 12:43

No, I want to get ("\?"), not ("\\?"). – hoangvu68 Jan 06 '13 at 12:55

score 0 · Answer 3 · answered Jan 06 '13 at 12:44

0

("\\?","") means that the '\' is escaped, otherwise '\?' would be interpreted as escape sequence.

answered Jan 06 '13 at 12:44

ConfusedProgrammer

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score 0 · Answer 4 · answered Jan 06 '13 at 12:47

0

？need not to be backslashed. So what you get is right and enough.

answered Jan 06 '13 at 12:47

mayaa

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Convert from string to tuple with "\" in python

4 Answers4