Welcome, guest | Sign In | My Account | Store | Cart

This is a useful bit of code for removing whitespace from a list of strings. For example, if you split a string, there might be superfluous whitespace.

Python, 42 lines
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
# striplist.py

# Take a list of string objects and return the same list
# stripped of extra whitespace.

def striplist(l):
    return([x.strip() for x in l])

# This may look a bit more elegant, but it is significantly slower than
# striplist(). This may be dur to the fact that it's using the string.strip()
# method.

from string import strip
def inefficient(l):
    return(map(strip, l))
del strip
# Another version of inefficient() using builtin strip()
def inefficient_as_well(l):
    return(map(lambda x: x.strip(), l))

# This is only slightly slower than or comparable to striplist()
def comparable(l)
    for x in xrange(len(l)):
        l[x] = l[x].strip()
    return(l)

# This is also on the same order as both comparabale() & striplist()
def comparable_as_well(l)
    tmp = []
    for x in len(l):
        tmp.append(x.strip())
    return(tmp)

# An example of a class that would have the strip method.  It inherits
# everything from "list", and adds a method, .strip()
# This is slower than striplist()

class StrippableList(list):
    def __init__(self,l=[]):
        list.__init__(self,l)
    def strip(self,char=None):
        return(StrippableList([x.strip(char) for x in self]))

This is a function that I use quite a bit, and so far is the fastest implementation I could come up with. Since Python has a high overhead for function calls, the most efficient way is to strip the elements you need from within your code. In fact, it may be faster to implement the [x.strip() for x in l] idiom right in your code.

My reason for getting into this was because I was having a huge problem with the speed of some of my code. Using profile showed me that the function calls I had going out to strip the list of strings was having a big impact on the speed of execution. Simple functions can have a big impact!

An alternative might be to add a .strip() method to the list class -- this might improve speed (by pushing the code into C). The class StrippableList() is an example in python (since I'm no C coder). It's slower than striplist(), however.

Created by Matthew Shomphe on Fri, 13 Jun 2003 (PSF)
Python recipes (4591)
Matthew Shomphe's recipes (1)

Required Modules

  • (none specified)

Other Information and Tasks