determine the type of a value which is represented as string in python

Question

When I read a comma seperated file or string with the csv parser in python all items are represented as a string. see example below.

import csv
a = "1,2,3,4,5"
r = csv.reader([a])
for row in r:
    d = row

d
['1', '2', '3', '4', '5']
type(d[0])
<type 'str'>

I want to determine for each value if it is a string, float, integer or date. How can I do this in python?

Answer 1

You could do something like this:

from datetime import datetime

tests = [
    # (Type, Test)
    (int, int),
    (float, float),
    (datetime, lambda value: datetime.strptime(value, "%Y/%m/%d"))
]

def getType(value):
     for typ, test in tests:
         try:
             test(value)
             return typ
         except ValueError:
             continue
     # No match
     return str

>>> getType('2010/1/12')
<type 'datetime.datetime'>
>>> getType('2010.2')
<type 'float'>
>>> getType('2010')
<type 'int'>
>>> getType('2013test')
<type 'str'>

The key is in the tests order, for example the int test should be before the float test. And for dates you can add more tests for formats you want to support, but obviously you can't cover all possible cases.