Determine the Kind (int, float) of Number a Python numeric literal represents?

Question

In case anyone is interested, this is a followup to Regular expression to match a Python integer literal.

The tokenize module is useful for breaking apart a Python expression, but tokenize.NUMBER is not very expressive, as it represents all kinds of number literals, for example, 1, 1l (in Python 2), 0xf2, 1e-10, 1.1, 0b101, 0o17, and 1j are all considered NUMBER (and also all the previous with uppercase letters). Is there a function in the standard library that tells me what kind of the above I have? I particularly care about if I have an integer or a float (complex is also considered float), but further expressiveness would be OK too :). Basically, I don't want to try to catch all possible number literals myself, as I already managed to do it wrong once.

Answer 1

Possibly ast.literal_eval?

type(ast.literal_eval(s))

Answer 2

You can use ast.literal_eval to parse any Python number format down to an int, float, or long:

>>> ast.literal_eval('1')
1
>>> ast.literal_eval('1l')
1L
>>> ast.literal_eval('0x2')
2
>>> ast.literal_eval('0b1101')
13

Bear in mind that there is no 'hex' or 'oct' or 'bin' type in Python. Those literal strings are immediately converted to their decimal equivalents.

This works pretty well:

def numtype(s):
    numtypes=[int,long,float,complex]

    try:
        n=ast.literal_eval(s)
    except SyntaxError:
        return None

    if type(n) not in numtypes:
        return None  
    else:
        return type(n)    

for t in ['1','0x1','0xf2','1e-10','0o7','1j', '0b1101']:
    print t, numtype(t)              

Prints:

1 <type 'int'>
0x1 <type 'int'>
0xf2 <type 'int'>
1e-10 <type 'float'>
0o7 <type 'int'>
1j <type 'complex'>
0b1101 <type 'int'>

If you really need to differentiate between the different decimal types, you could do something like:

def numtype(s):
    numtypes=[int,long,float,complex]

    try:
        n=ast.literal_eval(s)
    except SyntaxError:
        return None

    if type(n) not in numtypes:
        return None    

    if type(n) != int:
        return type(n)
    else:
        if 'x' in s.lower():
            return 'HEX'
        if 'o' in s.lower():
            return 'OCT'   
        if 'b' in s.lower():
            return 'BIN'     

        return int

Answer 3

def is_int(number_string):
    try:
        i = int(number_string)
    except ValueError:
        return False
    return True