strings = ["1 asdf 2", "25etrth", "2234342 awefiasd"] #and so on
Which is the easiest way to get [1, 25, 2234342]?
How can this be done without a regex module or expression like (^[0-9]+)?
5 Answers
One could write a helper function to extract the prefix:
def numeric_prefix(s):
n = 0
for c in s:
if not c.isdigit():
return n
else:
n = n * 10 + int(c)
return n
Example usage:
>>> strings = ["1asdf", "25etrth", "2234342 awefiasd"]
>>> [numeric_prefix(s) for s in strings]
[1, 25, 2234342]
Note that this will produce correct output (zero) when the input string does not have a numeric prefix (as in the case of empty string).
Working from Mikel's solution, one could write a more concise definition of numeric_prefix:
import itertools
def numeric_prefix(s):
n = ''.join(itertools.takewhile(lambda c: c.isdigit(), s))
return int(n) if n else 0
1 Comment
Mikhail M.
Thanks, "takewhile" is what I need
new = []
for item in strings:
new.append(int(''.join(i for i in item if i.isdigit())))
print new
[1, 25, 2234342]
5 Comments
Mikhail M.
But it will check each letter in string. "1 asdf 1" will turn into 11 instead of 1
NT3RP
If the string was "1 asdf 2" would the result be 1 or 2?
dawg
@CSZ: If the string is
"1 asdf 1" what should (or do you expect) the result to be? 1 or 11? These are your strings...
Mikel
See itertools.takewhile for one way to fix the
"1 asdf 2" problem.
rlibby
If you're going to give a list comprehension solution, might as well go all out (:
[int(x) for x in ["".join([c for c in s if c.isdigit()]) for s in strings]]Basic usage of regular expressions:
import re
strings = ["1asdf", "25etrth", "2234342 awefiasd"]
regex = re.compile('^(\d*)')
for s in strings:
mo = regex.match(s)
print s, '->', mo.group(0)
1asdf -> 1
25etrth -> 25
2234342 awefiasd -> 2234342
3 Comments
Steven Rumbalski
-1. Third line of question reads "How can this be done without a regex module or expression like (^[0-9]+)?" It's pretty obvious CSZ is asking for an answer that does not use
re.Steven Rumbalski
Agreed. But /that/ should have been your answer.
Building on sahhhm's answer, you can fix the "1 asdf 1" problem by using takewhile.
from itertools import takewhile
def isdigit(char):
return char.isdigit()
numbers = []
for string in strings:
result = takewhile(isdigit, string)
resultstr = ''.join(result)
if resultstr:
number = int(resultstr)
if number:
numbers.append(number)
1 Comment
Mikel
Note that Adeel Soomro's answer is probably simpler, provided it's OK for a string containing no digits to appear as
None in the result list.So you only want the leading digits? And you want to avoid regexes? Probably there's something shorter but this is the obvious solution.
nlist = []
for s in strings:
if not s or s[0].isalpha(): continue
for i, c in enumerate(s):
if not c.isdigit():
nlist.append(int(s[:i]))
break
else:
nlist.append(int(s))
"asdf"in the input? Should it be0, or not appear in the result list?