Generalized integer casting in Python

Question

Background

I have a string in Python which I want to convert to an integer. Normally, I would just use int:

>>> int("123")
123

Unfortunately, this method is not very robust, as it only accepts strings that match -?[0-9]+ (after removing any leading or trailing whitespace). For example, it can't handle input with a decimal point:

>>> int("123.45")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '123.45'

And it certainly can't handle this:

>>> int("123abc?!")

On the other hand, exactly this behavior can be had without any fuss in Perl, PHP, and even the humble QBasic:

INT(VAL("123abc"))   ' 123

Question

Here's my shortest effort at this "generalized int" in Python. It's 50 bytes, assuming that the original string is in s and the result should end up in i:

n="";i=0
for c in s:
 n+=c
 try:i=int(n)
 except:0

Fairly straightforward, but the try/except bit is ugly and long. Is there any way to shorten it?

Details

Answers need to do all of the following:

• Start with a string in s; end with its integer value in i.
• The integer is the first run of digits in the string. Everything after that is ignored, including other digits if they come after non-digits.
• Leading zeros in the input are valid.
• Any string that does not start with a valid integer has a value of 0.

The following features are preferred, though not required:

• A single - sign immediately before the digits makes the integer negative.
• Ignores whitespace before and after the number.
• Works equally well in Python 2 or 3.

(Note: my code above meets all of these criteria.)

Test cases

"0123"   -> 123
"123abc" -> 123
"123.45" -> 123
"abc123" -> 0
"-123"   -> -123 (or 0 if negatives not handled)
"-1-2"   -> -1 (or 0 if negatives not handled)
"--1"    -> 0
""       -> 0

Answer 1

Python 2, 47, 46

It's not as short as using regex, but I thought it was entertainingly obscure.

i=int(('0%sx'%s)[:~len(s.lstrip(str(1<<68)))])

-1 due to KSab – str with some large integer works better than the repr operator since it does not put an L on the end.

Answer 2

40 bytes

import re;i=int("0"+re.split("\D",s)[0])

and you can do negatives for 8 characters more:

import re;i=int((re.findall("^-?\d+",s)+[0])[0])