Python - Validate currency

What is the best way to validate an input as a currency (without any currency symbols) My val开发者_JAVA技巧id inputs can be only in the form of 40 or 40.12

---

How about simply using format() and try/except for wrong values?

>>> "{:.2f}".format(float("40.12"))
'40.12'
>>> "{:.2f}".format(float("40"))
'40.00'
>>> "{:.2f}".format(float("40.123"))
'40.12'
>>> try:
...     "{:.2f}".format(float("40.123€"))
... except ValueError:
...     "fail"
... 
'fail'

Note that it simply cuts any number behind the second number behind the decimal point. You should be more specific by showing us more examples with your desired behaviour.

---

You could use a regular expression:

re.match(r'\d+(?:[.]\d{2})?$', '40.12')

This returns a match object if the input is correct, or None if it isn't.

The above regex matches one or more digits optionally followed by a dot and exactly two more digits. This can be tweaked as required if I didn't capture your requirements precisely (the problem statement is somewhat open to interpretation).

---

I've been googling about an hour for proper way on how to do this. I haven't found any really good and safe way, and wrote regular expression below to match positive non-zero number with optional 1-2 digits after dot-separator:

re.match(r'^[1-9]\d*(\.\d{1,2})?$', val)

• ^ and $: without matching whole string there will be ways to fooling up the regex.
• [1-9]: first character always should be from 1 to 9
• \d*: after first digit any amount of digits allowed
• (\.\d{1,2})?: optional 1-2 digit fraction with dot-separator. Use [\.\,] instead of \. if multiple separator support is needed