Get type of data stored in a string in python

Question

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?

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
– Prasath, Commented Jul 12, 2013 at 21:57
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
– tobias_k, Commented Jul 12, 2013 at 21:57
@JonClements: most eval calls are inherently very dangerous, no? — inspectorG4dget
– inspectorG4dget, Commented Jul 12, 2013 at 21:58
It's limited to certain basic types and doesn't do execution - so will except rather than do anything untoward. In the case of the op this will be an unknown type or the value is left as.a string — Jon Clements
– Jon Clements, Commented Jul 12, 2013 at 22:01

perreal · Accepted Answer · 2013-07-12 22:04:14Z

15

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'>

answered Jul 12, 2013 at 22:04

perreal

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1 Comment

2rs2ts Over a year ago

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).

murftown · Accepted Answer · 2013-07-12 22:07:28Z

8

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')

edited Jul 12, 2013 at 22:07

answered Jul 12, 2013 at 22:01

murftown

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murftown Over a year ago

Glad to help, Prasath. Pretty much the same as perreal's answer.

jterrace · Accepted Answer · 2013-07-12 22:02:35Z

1

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'>

answered Jul 12, 2013 at 22:02

jterrace

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1 Comment

2rs2ts Over a year ago

Caveat: You have to do int before float otherwise you could do float(1) and it'd be just fine.

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