Develop Reference

How to extract string inside a string in python?

Need a solution for bellow code.
variable = ' "value" '
How to get variable = 'value'
Thanks

try:
variable.replace("\"","").strip()
replace replaces the double quotes with nothing (removes it) and strip() removes the trailing and leading spaces

You can try this:
s = ' "value" '
s = s[2:-2]
print(s)
Output:
value

Replace the " character with a space

I have a CSV file, where each comma delimited field is enclosed in " - eg. "fred", "bert", "blah". I am trying to use the replace function but can't seem to have it recognize the " character. example, if the record is in a string called buffer:
buffer.replace('\"','')

Add space between double quotes
p = '"fred", "bert", "blah"'
p.replace('\"'," ")
' fred , bert , blah '

Why do you escape the double quotes if it's inside single quotes ?
Try the following :
a = '"my string"'
a = a.replace('"',' ')
print(a)
#=> ' my string '

You are not replacing it with space firstly, but with empty string
Try using buffer.strip("\"")

Why are Python strings behaving funny?

I'm so confused... why/how is a different from b?! Why don't they print the same thing?
>>> a = '"'
>>> a
'"'
>>> b = "'"
>>> b
"'"

The strings are not presented differently. Their presentation is just adjusted to avoid having to quote the contained quote. Both ' and " are legal string literal delimiters.
Note that the contents of the string are very different. " is not the same string as '; a == b is (patently) False.
Python would have to use a \ backslash for the " or ' character otherwise. If you use both characters in a string, then python is forced to use quoting:
>>> '\'"'
'\'"'
>>> """Tripple quoted means you can use both without escaping them: "'"""
'Tripple quoted means you can use both without escaping them: "\''
As you can see, the string representation used by Python still uses single quotes and a backslash to represent that last string.

lexical analysis python

Recently I made the following observation:
>>> x= "\'"
>>> x
"'"
>>> y="'"
>>> y
"'"
>>> print x
'
>>> print y
'
Can anyone please explain why is it so. I am using python 2.7.x. I know well about escape sequences.
I want to do the following:
I have a string with single quotes in it and I have to enter it in a database so I need to replace the instance of single quote(') with a backslash followed by a single quote(\'). How can I achieve this.

Inside a pair of "", you don't need to escape the ' character. You can, of course, but as you've seen it's unnecessary and has no effect whatsoever.
It'd be necessary to escape if you were to write a ' inside a pair of '' or a " inside a pair of "":
x = '\''
y = "\""
EDIT :
Regarding the last part in the question, added after the edit:
I have a string with single quotes in it and I have to enter it in a database so I need to replace the instance of single quote(') with a backslash followed by a single quote(\'). How can I achieve this
Any of the following will work, notice the use of raw strings for avoiding the need to escape special characters:
v = "\\'"
w = '\\\''
x = r'\''
y = r"\'"
print v, w, x, y
> \' \' \' \'

Remove from python string

When you run something through popen in Python, the results come in from the buffer with the CR-LF decimal value of a carriage return (13) at the end of each line. How do you remove this from a Python string?

You can simply do
s = s.replace('\r\n', '\n')
to replace all occurrences of CRNL with just NL, which seems to be what you want.

buffer = "<text from your subprocess here>\r\n"
no_cr = buffer.replace("\r\n", "\n")

If they are at the end of the string(s), I would suggest to use:
buffer = "<text from your subprocess here>\r\n"
no_cr = buffer.rstrip("\r\n")
You can also use rstrip() without parameters which will remove whitespace as well.

replace('\r\n','\n') should work, but sometimes it just does not. How strange. Instead you can use this:
lines = buffer.split('\r')
cleanbuffer = ''
for line in lines: cleanbuffer = cleanbuffer + line

Actually, you can simply do the following:
s = s.strip()
This will remove any extraneous whitespace, including CR and LFs, leading or trailing the string.
s = s.rstrip()
Does the same, but only trailing the string.
That is:
s = ' Now is the time for all good... \t\n\r "
s = s.strip()
s now contains 'Now is the time for all good...'
s = s.rstrip()
s now contains ' Now is the time for all good...'
See http://docs.python.org/library/stdtypes.html for more.

You can do s = s.replace('\r', '') too.