newbie question: parse a variable inside an RE?

[joemacbusiness]

Hi All,

How do I parse a variable inside an RE?
What is the re.search() syntax when your
search string is a variable?
It's easy to parse hardcoded RE's but not
if you use a variable.

Here is my code, input and runtime:

$ cat test45.py
#!/usr/bin/python

import re

resp = raw_input('Selection: ')
newresp = resp.strip()
print "you chose ", newresp

fname = open('test44.in')
for I in fname:
# if re.search('^newresp', "%s"%(I)): # returns nothing
# if re.search(^newresp, "%s"%(I)): # syntax error
if re.search("^newresp", "%s"%(I)): # returns nothing
print I,

[jmccaughan@dhcppc2 work]$ cat test44.in
a1
b1
g1
g2
h1
h4
4g
5g
h5

$ python test45.py
Selection: g
you chose g
$

Thanks...

 

[Diez B. Roggisch]

Hi All,

How do I parse a variable inside an RE?
What is the re.search() syntax when your
search string is a variable?
It's easy to parse hardcoded RE's but not
if you use a variable.

Both are exactly equal in difficulty.

Here is my code, input and runtime:

$ cat test45.py
#!/usr/bin/python

import re

resp = raw_input('Selection: ')
newresp = resp.strip()
print "you chose ", newresp

fname = open('test44.in')
for I in fname:
# if re.search('^newresp', "%s"%(I)): # returns nothing
# if re.search(^newresp, "%s"%(I)): # syntax error
if re.search("^newresp", "%s"%(I)): # returns nothing
print I,

How should python know that you want the newresp being expanded? And not
that you want to search for the word "newresp"?


You need to use the *variable* newresp:

if re.search(newresp, I): ...

If you want to alter it to have a "^" prepended before you use it, you
need to do so:

newresp = "^" + newresp

And as show above,

"%s" % I

is nothing but I - no need for the string-interpolation.

Diez

 

[John Machin]

Both are exactly equal in difficulty.










How should python know that you want the newresp being expanded? And not
that you want to search for the word "newresp"?

You need to use the *variable* newresp:

if re.search(newresp, I): ...

If you want to alter it to have a "^" prepended before you use it, you
need to do so:

newresp = "^" + newresp

And as show above,

"%s" % I

is nothing but I - no need for the string-interpolation.

In fact what the OP is trying to do amounts to a convoluted version of
I.startswith(newresp) which probably isn't his real requirement
anyway :-(