How can I get the name of an object in Python

Question

Is there any way to get the name of an object in Python   For instance   my list    x  y  z    x  y  z have been previously defined  for bla in my list      print  handling object    name bla     lt --- what would go instead of  name         do something to bla   Edit  Some context   What I m actually doing is creating a list of functions that I can specify by the command line   I have   def fun1      pass def fun2     pass def fun3      pass  fun dict     fun1   fun1               fun2   fun2               fun3   fun3    I get the name of the function from the commandline and I want to call the relevant function   func name   parse commandline    fun dict func name      And the reason I want to have the name of the function is because I want to create fun dict without writing the names of the functions twice  since that seems like a good way to create bugs   What I want to do is   fun list    fun1  fun2  fun3    and I ll add more as the need arises  fun dict       fun dict name t    t for t in fun list     lt -- this is where I need the name function   This way I only need to write the function names once

User · Answer

Python has names which are mapped to objects in a hashmap called a namespace. At any instant in time, a name always refers to exactly one object, but a single object can be referred to by any arbitrary number of names. Given a name, it is very efficient for the hashmap to look up the single object which that name refers to. However given an object, which as mentioned can be referred to by multiple names, there is no efficient way to look up the names which refer to it. What you have to do is iterate through all the names in the namespace and check each one individually and see if it maps to your given object. This can easily be done with a list comprehension:

[k for k,v in locals().items() if v is myobj]

This will evaluate to a list of strings containting the names of all local "variables" which are currently mapped to the object myobj.

>>> a = 1
>>> this_is_also_a = a
>>> this_is_a = a
>>> b = "ligma"
>>> c = [2,3, 534]
>>> [k for k,v in locals().items() if v is a]

['a', 'this_is_also_a', 'this_is_a']

Of course locals() can be substituted with any dict that you want to search for names that point to a given object. Obviously this search can be slow for very large namespaces because they must be traversed in their entirety.

User · Answer

Here s another way to think about it   Suppose there were a name   function that returned the name of its argument   Given the following code   def f a       return a  b    x  c   b d   f c   e    f b   f c   f d     What should name e 2   return  and why

User · Answer

That s not really possible  as there could be multiple variables that have the same value  or a value might have no variable  or a value might have the same value as a variable only by chance   If you really want to do that  you can use  def variable for value value       for n v in globals   items            if v    value              return n     return None   However  it would be better if you would iterate over names in the first place   my list     x    y    z     x  y  z have been previously defined  for name in my list      print  handling variable    name     bla   globals   name        do something to bla    nbsp

User · Answer

You define a class and add the Unicode private function insert the class like  class example    def   init   self  name       self name   name    def   unicode   self       return self name   Of course you have to add extra variable self name which is the name of the object

User · Answer

Generally when you are wanting to do something like this  you create a class to hold all of these functions and name them with some clear prefix cmd  or the like   You then take the string from the command  and try to get that attribute from the class with the cmd  prefixed to it   Now you only need to add a new function method to the class  and it s available to your callers   And you can use the doc strings for automatically creating the help text   As described in other answers  you may be able to do the same approach with globals   and regular functions in your module to more closely match what you asked for   Something like this   class Tasks      def cmd doit self             do it here  func name   parse commandline   try      func   getattr  cmd     func name  Tasks    except AttributeError        bad command  exit or whatever func

User · Answer

As others have mentioned  this is a really tricky question  Solutions to this are not  one size fits all   not even remotely  The difficulty  or ease  is really going to depend on your situation   I have come to this problem on several occasions  but most recently while creating a debugging function  I wanted the function to take some unknown objects as arguments and print their declared names and contents  Getting the contents is easy of course  but the declared name is another story   What follows is some of what I have come up with   Return function name  Determining the name of a function is really easy as it has the   name   attribute containing the function s declared name   name of function   lambda x   x   name    def name of function arg       try          return arg   name       except AttributeError          pass    Just as an example  if you create the function def test function    pass  then copy function   test function  then name of function copy function   it will return test function   Return first matching object name   Check whether the object has a   name   attribute and return it if so  declared functions only   Note that you may remove this test as the name will still be in globals    Compare the value of arg with the values of items in globals   and return the name of the first match  Note that I am filtering out names starting with        The result will consist of the name of the first matching object otherwise None   def name of object arg         check   name   attribute  functions      try          return arg   name       except AttributeError          pass      for name  value in globals   items            if value is arg and not name startswith                   return name   Return all matching object names   Compare the value of arg with the values of items in globals   and store names in a list  Note that I am filtering out names starting with        The result will consist of a list  for multiple matches   a string  for a single match   otherwise None  Of course you should adjust this behavior as needed   def names of object arg       results    n for n  v in globals   items   if v is arg and not n startswith           return results 0  if len results  is 1 else results if results else None

User · Answer

I ran into this page while wondering the same question   As others have noted  it s simple enough to just grab the   name   attribute from a function in order to determine the name of the function  It s marginally trickier with objects that don t have a sane way to determine   name    i e  base primitive objects like basestring instances  ints  longs  etc   Long story short  you could probably use the inspect module to make an educated guess about which one it is  but you would have to probably know what frame you re working in traverse down the stack to find the right one  But I d hate to imagine how much fun this would be trying to deal with eval exec ed code     python2 whats my name again py needle   gt    b     a    b      needle   gt    lt function foo at 0x289d08ec gt     c     foo   needle   gt    lt function bar at 0x289d0bfc gt     f    bar      needle   gt    lt   main   a class instance at 0x289d3aac gt     e    d      needle   gt    lt function bar at 0x289d0bfc gt     f    bar          whats my name again py      usr bin env python  import inspect  class a class      def   init   self           pass  def foo        def bar            pass      a    b      b    b      c   foo     d   a class       e   d     f   bar       print  globals   inspect stack   0  0  f globals       print  locals   inspect stack   0  0  f locals       assert inspect stack   0  0  f globals    globals        assert inspect stack   0  0  f locals    locals         in a haystack   lambda  value    needle and key     needle       for needle in  a  foo  bar  d  f             print  needle   gt    r      needle             print  key for key  value in locals   iteritems   if in a haystack             print  key for key  value in globals   iteritems   if in a haystack       foo

User · Answer

Based on what it looks like you re trying to do you could use this approach  In your case  your functions would all live in the module foo  Then you could  import foo  func name   parse commandline   method to call   getattr foo  func name  result   method to call    Or more succinctly  import foo  result   getattr foo  parse commandline

User · Answer

Here is my answer  I am also using globals   items        def get name of obj obj  except word                 for name  item in globals   items                if item    obj and name    except word                  return name   I added except word because I want to filter off some word used in for loop   If you didn t add it  the keyword in for loop may confuse this function  sometimes the keyword like  each item  in the following case may show in the function s result  depends on what you have done to your loop   eg       for each item in  objA  objB  objC           get name of obj obj   each item     eg        gt  gt  gt  objA    1  2  3       gt  gt  gt  objB     a     b   thi is B     c        gt  gt  gt  for each item in  objA  objB               get name of obj each item               objA       objB       gt  gt  gt       gt  gt  gt       gt  gt  gt  for each item in  objA  objB               get name of obj each item               objA       objB       gt  gt  gt       gt  gt  gt       gt  gt  gt  objC      a1   a2         gt  gt  gt       gt  gt  gt  for item in  objA  objB  objC               get name of obj item               objA       item    lt  lt  lt  lt  lt  lt  lt  lt  lt  lt  --------- this is no good      item       gt  gt  gt  for item in  objA  objB               get name of obj item               objA       item       lt  lt  lt  lt  lt  lt  lt  lt --------this is no good      gt  gt  gt       gt  gt  gt  for item in  objA  objB  objC               get name of obj item   item                objA       objB    lt  lt  lt  lt  lt  lt  lt  lt  lt  lt --------- now it s ok      objC       gt  gt  gt    Hope this can help

User · Answer

Note that while  as noted  objects in general do not and cannot know what variables are bound to them  functions defined with def do have names in the   name   attribute  the name used in def    Also if the functions are defined in the same module  as in your example  then globals   will contain a superset of the dictionary you want    def fun1    pass def fun2    pass def fun3    pass  fun dict      for f in  fun1  fun2  fun3     fun dict f   name      f

User · Answer

If you are looking to get the names of functions or lambdas or other function-like objects that are defined in the interpreter  you can use dill source getname from dill   It pretty much looks for the   name   method  but in certain cases it knows other magic for how to find the name    or a name for the object   I don t want to get into an argument about finding the one true name for a python object  whatever that means    gt  gt  gt  from dill source import getname  gt  gt  gt    gt  gt  gt  def add x y         return x y       gt  gt  gt  squared   lambda x x  2  gt  gt  gt    gt  gt  gt  print getname add   add   gt  gt  gt  print getname squared   squared   gt  gt  gt    gt  gt  gt  class Foo object         def bar self  x           return x x x       gt  gt  gt  f   Foo    gt  gt  gt    gt  gt  gt  print getname f bar   bar   gt  gt  gt    gt  gt  gt  woohoo   squared  gt  gt  gt  plus   add  gt  gt  gt  getname woohoo   squared   gt  gt  gt  getname plus   add

User · Answer

This one-liner works  for all types of objects  as long as they are in globals   dict  which they should be   def name of global obj xx       return  objname for objname  oid in globals   items               if id oid   id xx   0    or  equivalently   def name of global obj xx       for objname  oid in globals   items            if oid is xx              return objname

User · Answer

Objects do not necessarily have names in Python  so you can t get the name  It s not unusual for objects to have a   name   attribute in those cases that they do have a name  but this is not a part of standard Python  and most built in types do not have one  When you create a variable  like the x  y  z above then those names just act as  quot pointers quot  or  quot references quot  to the objects  The object itself does not know what name you are using for it  and you can not easily  if at all  get the names of all references to that object  Update  However  functions do have a   name    unless they are lambdas  so  in that case you can do  dict   t   name    t  for t in fun list

User · Answer

And the reason I want to have the name of the function is because I want to create fun dict without writing the names of the functions twice  since that seems like a good way to create bugs    For this purpose you have a wonderful getattr function  that allows you to get an object by known name  So you could do for example   funcs py   def func1    pass def func2    pass   main py   import funcs option   command line option   getattr funcs  option

User · Answer

Use a reverse dict   fun dict     fun1   fun1               fun2   fun2               fun3   fun3   r dict   dict zip fun dict values    fun dict keys       The reverse dict will map each function reference to the exact name you gave it in fun dict  which may or may not be the name you used when you defined the function   And  this technique generalizes to other objects  including integers   For extra fun and insanity  you can store the forward and reverse values in the same dict   I wouldn t do that if you were mapping strings to strings  but if you are doing something like function references and strings  it s not too crazy

User · Answer

Variable names can be found in the globals   and locals   dicts  But they won t give you what you re looking for above   bla  will contain the value of each item of my list  not the variable

[python] How can I get the name of an object in Python?

Examples related to python

Examples related to introspection