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, Jul 12 '13 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, Jul 12 '13 at 21:57
@JonClements: most `eval` calls are inherently very dangerous, no? — inspectorG4dget, Jul 12 '13 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, Jul 12 '13 at 22:01
Check this question: http://stackoverflow.com/questions/379906/parse-string-to-float-or-int — Basel Shishani, Jul 12 '13 at 22:11

score 15 · Accepted Answer · answered Jul 12 '13 at 22:04

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 '13 at 22:04

perreal

94,503
21
155
181

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 '13 at 22:07

murftown · Answer 2 · 2013-07-12T22:07:28.717

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 '13 at 22:07

answered Jul 12 '13 at 22:01

murftown

1,287
1
10
13

Glad to help, Prasath. Pretty much the same as perreal's answer. – murftown Jul 12 '13 at 22:55

score 1 · Answer 3 · answered Jul 12 '13 at 22:02

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 '13 at 22:02

jterrace

64,866
22
157
202

2

Caveat: You have to do `int` before `float` otherwise you could do `float(1)` and it'd be just fine. – 2rs2ts Jul 12 '13 at 22:10

Get type of data stored in a string in python

3 Answers3