How to check if type of a variable is string?

Question

Is there a way to check if the type of a variable in python is a string, like:

isinstance(x,int);

for integer values?

Answer 1

In Python 3.x, the correct way to check if s is a string is

isinstance(s, str)

The bytes class isn't considered a string type in Python 3.

---

In Python 2.x, the correct check was

isinstance(s, basestring)

basestring is the abstract superclass of str and unicode. It can be used to test whether an object is an instance of either str or unicode.

Answer 2

I know this is an old topic, but being the first one shown on google and given that I don't find any of the answers satisfactory, I'll leave this here for future reference:

six is a Python 2 and 3 compatibility library which already covers this issue. You can then do something like this:

import six

if isinstance(value, six.string_types):
    pass # It's a string !!

Inspecting the code, this is what you find:

import sys

PY3 = sys.version_info[0] == 3

if PY3:
    string_types = str,
else:
    string_types = basestring,

Answer 3

In Python 3.x or Python 2.7.6

if type(x) == str:

Answer 4

you can do:

var = 1
if type(var) == int:
   print('your variable is an integer')

or:

var2 = 'this is variable #2'
if type(var2) == str:
    print('your variable is a string')
else:
    print('your variable IS NOT a string')

hope this helps!

Answer 5

Use type() or isinstance()

I don't know why not a single answer before me contains this simple type(my_variable) is str syntax, but using type() like this seems the most-logical and simple to me, by far:

(tested in Python3):

# Option 1: check to see if `my_variable` is of type `str`
type(my_variable) is str

# Option 2: check to see if `my_variable` is of type `str`, including
# being a subclass of type `str` (ie: also see if `my_variable` is any object 
# which inherits from `str` as a parent class)
isinstance(my_variable, str)

The Python type() built-in function documentation is here: https://docs.python.org/3/library/functions.html#type. It states, in part, the following. Notice the note about isinstance():

class type(object)
class type(name, bases, dict, **kwds)

With one argument, return the type of an object. The return value is a type object and generally the same object as returned by object.__class__.

The isinstance() built-in function is recommended for testing the type of an object, because it takes subclasses into account.

So, if you're checking the type of a class object instead of a simple variable, and you need to take subclasses into account, then use isinstance() instead. See its documentation here: https://docs.python.org/3/library/functions.html#isinstance.

Example code:

my_str = "hello"
my_int = 7

print(type(my_str) is str)
print(type(my_int) is str)

print()
print(isinstance(my_str, str))
print(isinstance(my_int, str))

Output:

True
False

True
False

Answer 6

The type module also exists if you are checking more than ints and strings. http://docs.python.org/library/types.html

Answer 7

Edit based on better answer below. Go down about 3 answers and find out about the coolness of basestring.

Old answer: Watch out for unicode strings, which you can get from several places, including all COM calls in Windows.

if isinstance(target, str) or isinstance(target, unicode):

Answer 8

since basestring isn't defined in Python3, this little trick might help to make the code compatible:

try: # check whether python knows about 'basestring'
   basestring
except NameError: # no, it doesn't (it's Python3); use 'str' instead
   basestring=str

after that you can run the following test on both Python2 and Python3

isinstance(myvar, basestring)

Answer 9

Python 2 / 3 including unicode

from __future__ import unicode_literals
from builtins import str  #  pip install future
isinstance('asdf', str)   #  True
isinstance(u'asdf', str)  #  True

http://python-future.org/overview.html

Answer 10

Lots of good suggestions provided by others here, but I don't see a good cross-platform summary. The following should be a good drop in for any Python program:

def isstring(s):
    # if we use Python 3
    if (sys.version_info[0] >= 3):
        return isinstance(s, str)
    # we use Python 2
    return isinstance(s, basestring)

In this function, we use isinstance(object, classinfo) to see if our input is a str in Python 3 or a basestring in Python 2.

Answer 11

So,

You have plenty of options to check whether your variable is string or not:

a = "my string"
type(a) == str # first 
a.__class__ == str # second
isinstance(a, str) # third
str(a) == a # forth
type(a) == type('') # fifth

This order is for purpose.

Answer 12

Also I want notice that if you want to check whether the type of a variable is a specific kind, you can compare the type of the variable to the type of a known object.

For string you can use this

type(s) == type('')

Answer 13

Alternative way for Python 2, without using basestring:

isinstance(s, (str, unicode))

But still won't work in Python 3 since unicode isn't defined (in Python 3).

Answer 14

Here is my answer to support both Python 2 and Python 3 along with these requirements:

• Written in Py3 code with minimal Py2 compat code.
• Remove Py2 compat code later without disruption. I.e. aim for deletion only, no modification to Py3 code.
• Avoid using six or similar compat module as they tend to hide away what is trying to be achieved.
• Future-proof for a potential Py4.

---

import sys
PY2 = sys.version_info.major == 2

# Check if string (lenient for byte-strings on Py2):
isinstance('abc', basestring if PY2 else str)

# Check if strictly a string (unicode-string):
isinstance('abc', unicode if PY2 else str)

# Check if either string (unicode-string) or byte-string:
isinstance('abc', basestring if PY2 else (str, bytes))

# Check for byte-string (Py3 and Py2.7):
isinstance('abc', bytes)

Answer 15

a = '1000' # also tested for 'abc100', 'a100bc', '100abc'

isinstance(a, str) or isinstance(a, unicode)

returns True

type(a) in [str, unicode]

returns True

Answer 16

If you do not want to depend on external libs, this works both for Python 2.7+ and Python 3 (http://ideone.com/uB4Kdc):

# your code goes here
s = ["test"];
#s = "test";
isString = False;

if(isinstance(s, str)):
    isString = True;
try:
    if(isinstance(s, basestring)):
        isString = True;
except NameError:
    pass;

if(isString):
    print("String");
else:
    print("Not String");

Answer 17

You can simply use the isinstance function to make sure that the input data is of format string or unicode. Below examples will help you to understand easily.

>>> isinstance('my string', str)
True
>>> isinstance(12, str)
False
>>> isinstance('my string', unicode)
False
>>> isinstance(u'my string',  unicode)
True

Answer 18

Summarizing:

There doesn't seem to be a portable way to do it if you want both Python2 and Python3, and want to include unicode as well. I wound up using this idiom:

# Near the top of my program
if sys.version_info[0] >= 3:
    basestring = str

Then any time I want to test an object to see if it's a string:

if isinstance(obj, basestring):
    ...

Frankly, I'm a little shocked that Python3 dropped basestring as well as types.StringTypes. I see no reason to drop them, and keeping either of them would have made this problem solveable.

Answer 19

s = '123'
issubclass(s.__class__, str)

Answer 20

This is how I do it:

if type(x) == type(str()):

Answer 21

I've seen:

hasattr(s, 'endswith') 

Answer 22

>>> thing = 'foo'
>>> type(thing).__name__ == 'str' or type(thing).__name__ == 'unicode'
True