[ACCEPTED]-regex for character appearing at most once-regex
[^.]*\.?[^.]*$
And be sure to match, don't search
>>> dot = re.compile("[^.]*\.[^.]*$")
>>> dot.match("fooooooooooooo.bar")
<_sre.SRE_Match object at 0xb7651838>
>>> dot.match("fooooooooooooo.bar.sad") is None
True
>>>
Edit:
If you consider 1 only integers and decimals, it's even easier:
def valid(s):
return re.match('[0-9]+(\.[0-9]*)?$', s) is not None
assert valid("42")
assert valid("13.37")
assert valid("1.")
assert not valid("1.2.3.4")
assert not valid("abcd")
No regexp is needed, see str.count():
str.count(sub[, start[, end]])Return the number 4 of non-overlapping occurrences of substring 3 sub in the range [start, end]. Optional 2 arguments start and end are interpreted 1 as in slice notation.
>>> "A.B.C.D".count(".")
3
>>> "A/B.C/D".count(".")
1
>>> "A/B.C/D".count(".") == 1
True
>>>
You can use:
re.search('^[^.]*\.?[^.]*$', 'this.is') != None
>>> re.search('^[^.]*\.?[^.]*$', 'thisis') != None
True
>>> re.search('^[^.]*\.?[^.]*$', 'this.is') != None
True
>>> re.search('^[^.]*\.?[^.]*$', 'this..is') != None
False
(Matches period zero or one 1 times.)
While period is special char it must be 3 escaped. So "\.+" should work.
EDIT:
Use 2 '?' instead of '+' to match one or zero 1 repetitions. Have a look at: re — Regular expression operations
If the period should exist only once in 6 the entire string, then use the ? operator:
^[^.]*\.?[^.]*$
Breaking 5 this down:
^matches the beginning of the string[^.]matches zero or more characters that are not periods\.?matches the period character (must be escaped with\as it's a reserved char) exactly 0 or 1 times[^.]*is the same pattern used in 2 above$matches the end of the string
As an aside, personally I wouldn't 4 use a regular expression for this (unless 3 I was checking other aspects of the string 2 for validity too). I would just use the 1 count function.
Why do you need to check? If you have a 3 number in a string, I now guess you will 2 want to handle it as a number soon. Perhaps 1 you can do this without Looking Before You Leap:
try:
value = float(input_str)
except ValueError:
...
else:
...
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