What is the Pythonic Way of Differentiating Between a String and a List?

Question

For my program I have a lot of places where an object can be either a string or a list containing strings and other similar lists. These are generally read from a JSON file. They both need to be treated differently. Right now, I am just using isinstance, but that does not feel like the most pythonic way of doing it, so does anyone have a better way of doing it?

Asked By: Nikwin

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Source

Answer 1

You can use types module:

import types
if type(ls) == types.ListType:
    #your code for list objects here

Answered By: Mustafa Zengin

Answer 2

Using isinstance:

On Python>=2.3 a string may be a str or unicode type. To check both cases:

if isinstance(a,basestring): # same as isinstance(obj, (str, unicode))
   print "Object is a string"

From Python 3 only one string type exists, so instead of basestring you should use str:

if isinstance(a,str):
   print "Object is a string"

Answered By: zoli2k

Answer 3

No need to import modules, isinstance(), str and unicode (versions before 3 — there’s no unicode in 3!) will do the job for you.

Python 2.x:

Python 2.6.1 (r261:67515, Feb 11 2010, 00:51:29) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> isinstance(u'', (str, unicode))
True
>>> isinstance('', (str, unicode))
True
>>> isinstance([], (str, unicode))
False

>>> for value in ('snowman', u'☃ ', ['snowman', u'☃ ']):
...     print type(value)
... 
<type 'str'>
<type 'unicode'>
<type 'list'>

Python 3.x:

Python 3.2 (r32:88445, May 29 2011, 08:00:24) 
[GCC 4.2.1 (Apple Inc. build 5664)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> isinstance('☃ ', str)
True
>>> isinstance([], str)
False

>>> for value in ('snowman', '☃ ', ['snowman', '☃ ']):
...     print(type(value))
... 
<class 'str'>
<class 'str'>
<class 'list'>

From PEP008:

Object type comparisons should always use isinstance() instead of comparing types directly.

Answered By: johnsyweb

Answer 4

Since Python3 no longer has unicode or basestring, in this case ( where you are expecting either a list or a string) it’s better to test against list

if isinstance(thing, list):
    # treat as list
else:
    # treat as str/unicode

as that is compatible with both Python2 and Python3

Answered By: John La Rooy

Answer 5

As I like to keep things simple, here is the shortest form that is compatible with both 2.x and 3.x:

# trick for py2/3 compatibility
if 'basestring' not in globals():
   basestring = str

v = "xx"

if isinstance(v, basestring):
   print("is string")

Answered By: sorin

Answer 6

Another method, using the practice of “It’s better to ask forgiveness than permission,” duck-typing being generally preferred in Python, you could try to do what you want first, e.g.:

try:
    value = v.split(',')[0]
except AttributeError:  # 'list' objects have no split() method
    value = v[0]

Answered By: knickum

What is the Pythonic Way of Differentiating Between a String and a List?

Question:

Answers:

Python 2.x:

Python 3.x: