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up vote 5 down vote favorite

Is there any way to understand what data type that a string holds... The question is of little logic but see below cases

varname = '444'
somefunc(varname) => int

varname = 'somestring'
somefunc(varname) => String

varname = '1.2323'
somefunc(varname) => float

My Case: I get a mixed data in a list but they're in string format.

myList = ['1', '2', '1.2', 'string']

I'm looking for a generic way to understand whats their data so that i can add respective comparison. Since they're already converted to string format, I cant really call the list (myList) as mixed data... but still is there a way?

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I tried type(eval('123')) => int, but type(eval('somename')) would fail as it cant be evaluated... also would work wrong if there is a variable named somename – Prasath Jul 12 at 21:57
1  
If you have just a few types to test, like the basic data types and string, then yes (just try to cast them). Otherwise, no. – tobias_k Jul 12 at 21:57
1  
You should really edit your OP instead of commenting on it – inspectorG4dget Jul 12 at 21:58
1  
Try ast.literal_eval – Jon Clements Jul 12 at 21:58
@JonClements: most eval calls are inherently very dangerous, no? – inspectorG4dget Jul 12 at 21:58
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3 Answers

up vote 14 down vote accepted 
from ast import literal_eval

def str_to_type(s):
    try:
        k=literal_eval(s)
        return type(k)
    except:
        return type(s)


l = ['444', '1.2', 'foo', '[1,2]', '[1']
for v in l:
    print str_to_type(v)

Output

<type 'int'>
<type 'float'>
<type 'str'>
<type 'list'>
<type 'str'>
share|improve this answer
Will work for most "primitive" types. Won't work for anything more complex, such as trying to get the type of a variable which happens to be a function object (like a lambda). – 2rs2ts Jul 12 at 22:07
this code thinks it's a string – perreal Jul 12 at 22:08
Thanks perreal!!! This would work for my current data. – Prasath Jul 12 at 22:27
up vote 6 down vote

You can use ast.literal_eval() and type():

import ast
stringy_value = '333'
try:
    the_type = type(ast.literal_eval(stringy_value))
except:
    the_type = type('string')
share|improve this answer
2  
Won't work on strings. – 2rs2ts Jul 12 at 22:04
1  
That's true actually, see my edit. – murftown Jul 12 at 22:06
1  
You're good to go now :) – 2rs2ts Jul 12 at 22:08
1  
Thanks murftown!!! this is exactly what i'm looking for!!! – Prasath Jul 12 at 22:28
Glad to help, Prasath. Pretty much the same as perreal's answer. – murftown Jul 12 at 22:55
up vote 1 down vote

I would just try different types, in the right order:

>>> def detect(s):
...     try:
...         return type(int(s))
...     except (TypeError, ValueError):
...         pass
...     try:
...         return type(float(s))
...     except (TypeError, ValueError):
...         pass
...     return type(s)
... 
>>> detect('3')
<type 'int'>
>>> detect('3.4')
<type 'float'>
>>> detect('foo')
<type 'str'>
share|improve this answer
2  
Caveat: You have to do int before float otherwise you could do float(1) and it'd be just fine. – 2rs2ts Jul 12 at 22:10

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