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Nov 4th, 2009

Help with string formatting

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Hi,

I need to read input from 2 different files, take text from both, combine it, then print it to a third file. That part is easy. What I have a problem with is that some of the text I read in have special characters that need to be escaped.

How can I handle those characters?

Any help would be appreciated, but I would obviously prefer a snippet of code I could use.

Thanks!

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P00dle

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Nov 4th, 2009

Re: Help with string formatting

You can use regular expressions and the re.sub function, like this

python Syntax (Toggle Plain Text)
import re
 
special = re.compile(r"[etn]")
 
def escape(match):
    return "\\" + match.group(0)
 
if __name__ == "__main__":
    text = "This is a test sentence."
    print text
    print special.sub(escape, text)
 
r""" my output --->
This is a test sentence.
This is a \t\es\t s\e\n\t\e\nc\e.
"""
import re

special = re.compile(r"[etn]")

def escape(match):
    return "\\" + match.group(0)

if __name__ == "__main__":
    text = "This is a test sentence."
    print text
    print special.sub(escape, text)

r""" my output --->
This is a test sentence.
This is a \t\es\t s\e\n\t\e\nc\e.
"""

Gribouillis

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Nov 4th, 2009

Re: Help with string formatting

Click to Expand / Collapse Quote originally posted by Gribouillis ...

You can use regular expressions and the re.sub function

Thanks!

I am going to try it now, and will let you know if it has worked, or not.

P00dle

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Nov 4th, 2009

Re: Help with string formatting

The code you supplied works just fine on its own. I need to be able to use it in a different situation.

If it's not too much trouble, would you mind explaining step-by-step what the code does please?

Thank you

P00dle

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Re: Help with string formatting

Click to Expand / Collapse Quote originally posted by P00dle ...

If it's not too much trouble, would you mind explaining step-by-step what the code does please?

The statement

python Syntax (Toggle Plain Text)
special = re.compile(r"[etn]")
special = re.compile(r"[etn]")

creates a regular expression object, which represents the set of characters 'e', 't' or 'n'. When

python Syntax (Toggle Plain Text)
special.sub(escape, text)
special.sub(escape, text)

is executed, all the occurrences of these characters are matched in the text and replaced by the output of the function 'escape'. A new string is returned.
The function 'escape' takes a 'match object' as argument which represents a match of the regex in a string and returns the text of the match preceded by a backslash.

Gribouillis

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Re: Help with string formatting

Wow!

That explains so much, thanks! I've written my own snippet, much like yours:

Python Syntax (Toggle Plain Text)
import re
 
foo = open("PREFIX.txt", "r+")
text = foo.read
foo.close()
 
special = re.compile(r"\\")
 
def escape(match):
    return "\\" + match.group(0)            
 
if __name__ == "__main__":
    out = open("WRITE.txt", "w")
    out.write(str(text))
    out.write(special.sub(escape, text))
    out.close()
import re

foo = open("PREFIX.txt", "r+")
text = foo.read
foo.close()

special = re.compile(r"\\")

def escape(match):
    return "\\" + match.group(0)            

if __name__ == "__main__":
    out = open("WRITE.txt", "w")
    out.write(str(text))
    out.write(special.sub(escape, text))
    out.close()

The following error appears, however(I am running it via the command console):
TraceBack (most recent call last):
File "advanced,py", line 15, in (module)
out.writeout.write(str(special.sub(escape, text)))
TypeError: expected string or buffer

I've also tried to use it run it while line 15 looked like this: out.write(special.sub(escape, text))

I have only started using Python yesterday, but the company needs me to use it now, for this, so please bear that in mind...

Thank you for the help, hopefully you can assist withthis as well.

P00dle

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Nov 4th, 2009

Re: Help with string formatting

Wow!

That explains so much, thanks! I've written my own snippet, much like yours:

Python Syntax (Toggle Plain Text)
import re
 
foo = open("PREFIX.txt", "r+")
text = foo.read
foo.close()
 
special = re.compile(r"\\")
 
def escape(match):
    return "\\" + match.group(0)            
 
if __name__ == "__main__":
    out = open("WRITE.txt", "w")
    out.write(str(text))
    out.write(special.sub(escape, text))
    out.close()
import re

foo = open("PREFIX.txt", "r+")
text = foo.read
foo.close()

special = re.compile(r"\\")

def escape(match):
    return "\\" + match.group(0)            

if __name__ == "__main__":
    out = open("WRITE.txt", "w")
    out.write(str(text))
    out.write(special.sub(escape, text))
    out.close()

P00dle

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Nov 4th, 2009

Re: Help with string formatting

Click to Expand / Collapse Quote originally posted by P00dle ...

Wow!

That explains so much, thanks! I've written my own snippet, much like yours:
Python Syntax (Toggle Plain Text)
foo = open("PREFIX.txt", "r+")
text = foo.read
foo = open("PREFIX.txt", "r+") text = foo.read

You must CALL the read method to get the file's content

python Syntax (Toggle Plain Text)
text = foo.read()
text = foo.read()

Also please mark your other thread with the same error as solved.

Last edited by Gribouillis; Nov 4th, 2009 at 5:16 am.

Gribouillis

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Nov 4th, 2009

Re: Help with string formatting

You are my Python hero!

Thanks a lot. Slapped myself.

P00dle

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