How to find out if a Python object is a string

Question

How can I check if a Python object is a string  either regular or Unicode

User · Answer

isinstance your object  basestring    will be True if your object is indeed a string-type   str  is reserved word   my apologies  the correct answer is using  basestring  instead of  str  in order of it to include unicode strings as well - as been noted above by one of the other responders

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If one wants to stay away from explicit type-checking  and there are good reasons to stay away from it   probably the safest part of the string protocol to check is   str maybe string     maybe string   It won t iterate through an iterable or iterator  it won t call a list-of-strings a string and it correctly detects a stringlike as a string    Of course there are drawbacks  For example  str maybe string  may be a heavy calculation  As so often  the answer is it depends   EDIT  As  Tcll points out in the comments  the question actually asks for a way to detect both unicode strings and bytestrings  On Python 2 this answer will fail with an exception for unicode strings that contain non-ASCII characters  and on Python 3 it will return False for all bytestrings

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if type varA     str or type varB     str      print  string involved    from  EDX - online course MITx  6 00 1x Introduction to Computer Science and Programming Using Python

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Python 3  In Python 3 x basestring is not available anymore  as str is the sole string type  with the semantics of Python 2 x s unicode    So the check in Python 3 x is just   isinstance obj to test  str    This follows the fix of the official 2to3 conversion tool  converting basestring to str

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Python 2  Use isinstance obj  basestring  for an object-to-test obj   Docs

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Its simple  use the following code  we assume the object mentioned to be obj -  if type obj     str      print  It is a string   else      print  It is not a string

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I might deal with this in the duck-typing style  like others mention   How do I know a string is really a string  well  obviously by converting it to a string   def myfunc word       word   unicode word            If the arg is already a string or unicode type  real word will hold its value unmodified   If the object passed implements a   unicode   method  that is used to get its unicode representation   If the object passed cannot be used as a string  the unicode builtin raises an exception

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For a nice duck-typing approach for string-likes that has the bonus of working with both Python 2 x and 3 x   def is string obj       try          obj              return True     except TypeError          return False   wisefish was close with the duck-typing before he switched to the isinstance approach  except that    has a different meaning for lists than   does

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Python 2 and 3   cross-compatible   If you want to check with no regard for Python version  2 x vs 3 x   use six  PyPI  and its string types attribute   import six  if isinstance obj  six string types       print  obj is a string      Within six  a very light-weight single-file module   it s simply doing this   import sys PY3   sys version info 0     3  if PY3      string types   str else      string types   basestring

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In order to check if your variable is something you could go like   s  Hello World  if isinstance s str    do something here    The output of isistance will give you a boolean True or False value so you can adjust accordingly  You can check the expected acronym of your value by initially using      type s  This will return you type  str  so you can use it in the isistance function

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I found this ans more pythonic   if type aObject  is str       do your stuff here     pass   since type objects are singleton  is can be used to do the compare the object to the str type

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This evening I ran into a situation in which I thought I was going to have to check against the str type  but it turned out I did not    My approach to solving the problem will probably work in many situations  so I offer it below in case others reading this question are interested  Python 3 only       NOTE  fields is an object that COULD be any number of things  including    - a single string-like object   - a string-like object that needs to be converted to a sequence of    string-like objects at some separator  sep   - a sequence of string-like objects def getfields  fields  sep      validator lambda f  True          Take a field sequence definition and yield from a validated      field sequence  Accepts a string  a string with separators        or a sequence of strings        if fields          try                single unpack in the case of a single argument             fieldseq    fields             try                    convert to string sequence if string                 fieldseq   fieldseq split sep              except AttributeError                    not a string  assume other iterable                 pass         except ValueError                not a single argument and not a string             fieldseq   fields         invalid fields    field for field in fieldseq if not validator field           if invalid fields              raise ValueError  One or more field names is invalid  n                                  r   format invalid fields       else          raise ValueError  No fields were provided       try          yield from fieldseq     except TypeError as e          raise ValueError  Single field argument must be a string                            or an interable   from e   Some tests    from   import getfields  def test getfields novalidation        result     a    b       assert list getfields  a b       result     assert list getfields  a b   sep          result     assert list getfields  a    b       result     assert list getfields   a    b        result

User · Answer

Python 2  To check if an object o is a string type of a subclass of a string type   isinstance o  basestring    because both str and unicode are subclasses of basestring   To check if the type of o is exactly str   type o  is str   To check if o is an instance of str or any subclass of str   isinstance o  str    The above also work for Unicode strings if you replace str with unicode   However  you may not need to do explicit type checking at all    Duck typing  may fit your needs   See http   docs python org glossary html term-duck-typing   See also What   s the canonical way to check for type in python

User · Answer

You can test it by concatenating with an empty string   def is string s     try      s         except      return False   return True   Edit   Correcting my answer after comments pointing out that this fails with lists  def is string s     return isinstance s  basestring

[python] How to find out if a Python object is a string?

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