On 2015-01-12 00:04, Mark Lawrence wrote:
On 11/01/2015 23:07, Thomas 'PointedEars' Lahn wrote:
Store Makhzan wrote:
I have this script which can calculate the total of numbers given in a
string […]
total = 0
for c in '0123456789':
total += int(c)
print total
[…]
How should I modify this script to find the total of if the numbers given
in the string form have decimal places? That is, how do I need to modify
this line: […]
for c in '1.32, 5.32, 4.4, 3.78':
[…] to find the total of these given numbers.
The original script already does not do what it advertises. Instead, it
iterates over the characters of the string, attempts to convert each to an
integer and then computes the sum. That is _not_ “calculate the total of
numbers given in a string”.
A solution has been presented, but it is not very pythonic because the
original code was not; that should have been
### Ahh, Gauß ;-)
print(sum(map(lambda x: int(x), list('0123456789'))))
### --------------------------------------------------------------------
Also, it cannot handle non-numeric strings well. Consider this instead:
### --------------------------------------------------------------------
from re import findall
s = '1.32, 5.32, 4.4, 3.78'
print(sum(map(lambda x: float(x), findall(r'-?\d+\.\d+', s))))
### --------------------------------------------------------------------
But if you are sure that except for the comma separator there are only
numeric strings, it is more efficient to use re.split() instead of
re.findall() here.
Aside:
I thought I had more than a fair grasp of regular expressions, but I am
puzzled by
| $ python3
| Python 3.4.2 (default, Dec 27 2014, 13:16:08)
| [GCC 4.9.2] on linux
| >>> from re import findall
| >>> s = '1.32, 5.32, 4.4, 3.78'
| >>> findall(r'-?\d+(\.\d+)?', s)
| ['.32', '.32', '.4', '.78']
Why does this more flexible pattern not work as I expected in Python 3.x,
but virtually everywhere else?
And why this?
| >>> findall(r'-?\d+\.\d+', s)
| ['1.32', '5.32', '4.4', '3.78']
| >>> findall(r'-?\d+(\.\d+)', s)
| ['.32', '.32', '.4', '.78']
Feature? Bug?
I can't tell you as I avoid regexes like I avoid the plague. Having
said that I do know that there loads of old bugs on the bug tracker,
many of which are fixed in the "new" regex module that's available here
https://pypi.python.org/pypi/regex/
It's not a bug.
re.findall returns the capture groups, if present, or the entire match
if there are no capture groups.
In this instance, it's better to use a non-capture group:
findall(r'-?\d+(?:\.\d+)', s)
It's all in the docs! :-)
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