My very first python program, need help

WP invalid at invalid.invalid
Sun Aug 10 15:52:37 CEST 2008

Hello, below is my very first python program. I have some questions 
regarding it and would like comments in general. I won't be able to get 
my hands on a good python book until tomorrow at the earliest. The 
program takes a string and sums all numbers inside it. I'm testing with 
the following string: "123xx,22! p1" which should yield a sum of 123 + 
22 + 1 = 146. My solution to this exercise was to write a function that 
takes a string and splits it into a list of numbers and then I will sum 
up the numbers in the list. In fact, I wrote two versions of this 
function: One uses a for loop to replace all characters that is not a 
digit and not a space with a space. That should leave me with the 
numbers intact and with only spaces separating these numbers. Then I 
call split to get a list of numbers (here I discovered I must not use a 
sep equal to ' ' or the returned list would contain empty strings as 
well). This is calculate_sum_1() and look at the comment in the code to 
see what worries me there. The second one uses regular expressions and 
the problem I have with that is that I get a list of containing not just 
the numbers but empty strings as well. I'm working around that in my 
loop that sums the numbers but it would be better to not have these 
empty string in the list in the first place. Here's the code:

import re

def calculate_sum_1(str):
     for c in str:
         if c.isdigit() == False and c != ' ':
             # That we assign to the variable we're looping over worries 
             str = str.replace(c, ' ')

     mylist = str.split()

     print "(for loop version) mylist after replace() and split() = ", 

     sum = 0

     for item in mylist:
        sum += long(item)

     return sum

def calculate_sum_2(str):
     #print "In replace_nondigits_2(), str = ", str
     p = re.compile('[^0-9]')

     mylist = p.split(str)

     print "(regex version) mylist after calling split(): ", mylist

     sum = 0

     for item in mylist:
         if item.isdigit():
             sum += long(item)

     return sum

str = "123xx,22! p1" # Sum = 123 + 22 + 1 = 146

print "str = ", str

print "calculate_sum_1(str): %d" % calculate_sum_1(str)
print "calculate_sum_2(str): %d" % calculate_sum_2(str)

The output when run is:
str =  123xx,22! p1
(for loop version) mylist after replace() and split() =  ['123', '22', '1']
calculate_sum_1(str): 146
(regex version) mylist after calling split():  ['123', '', '', '22', '', 
'', '1']
calculate_sum_2(str): 146

Hope I made some sense and thanks for reading!

- Eric (WP)

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