Check if string is a real number [duplicate]

This question already has answers here: 开发者_JAVA百科 How do I parse a string to a float or int? (32 answers) Closed last month.

Is there a quick way to find if a string is a real number, short of reading it a character at a time and doing isdigit() on each character? I want to be able to test floating point numbers, for example 0.03001.

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If you mean an float as a real number this should work:

def isfloat(str):
    try: 
        float(str)
    except ValueError: 
        return False
    return True

Note that this will internally still loop your string, but this is inevitable.

---

>>> a = "12345" # good number
>>> int(a)
12345
>>> b = "12345G" # bad number
>>> int(b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '12345G'

You can do that:

def isNumber(s):
    try:
        int(s)
    except ValueError:
        return False
    return True

If you want a float number, replace int by float (thanks to @cobbal).

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There is also another way using regular expression:

import re

def is_float(str):
    if re.match(r"\d+\.*\d*", str):
        return True
    else:
        return False

---

There is a more precise regexp of the real numbers:

"^[-+]?[0-9]*\.?[0-9]+(e[-+]?[0-9]+)?$"

And some check for this regexp:

realnum=re.compile("^[-+]?[0-9]*\.?[0-9]+(e[-+]?[0-9]+)?$")

["yes" if realnum.match(test) else "no" for test in ["12", "+12", "-12", "-3.14", ".314e1", "+.01e-12", "+22.134e+2"]]
['yes', 'yes', 'yes', 'yes', 'yes', 'yes', 'yes']

["yes" if realnum.match(test) else "no" for test in ["..12", "+-12", "-12.", "-3.14p", ".314e1.9", "+. 01e-12", "+22.134e"]]
['no', 'no', 'no', 'no', 'no', 'no', 'no']

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Method to verify real number:

def verify_real_number(item):
""" Method to find if an 'item'is real number"""

item = str(item).strip()
if not(item):
    return False
elif(item.isdigit()):
    return True
elif re.match(r"\d+\.*\d*", item) or re.match(r"-\d+\.*\d*", item):
    return True
else:
    return False

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Defining a function to do this is the right approach, although it's a shame that Python does not already provide such a function.

I'm not a fan of using try ... except for this, because it was drilled into me that "exceptions are for exceptional circumstances", and not for control flow.

A one-line solution (if you ever want it, although it is less efficient, except for the regex answers) is

lambda x: all(n < 2 and i.isdigit() for n, i in enumerate(x.split('.')))

If you are going to encounter decimals written as 1. or .01, then simply add a length check

lambda x: all(n < 2 and (i.isdigit() or len(i) == 0) for n, i in enumerate(x.split('.')))

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if you wanna check both integer and float numbers, you can check this out

def isDigit(str):
    try:
        int(str) or float(str)
    except ValueError:
        return False
    return True