Convert Variable Name to String

Question

I would like to convert a python variable name into the string equivalent as shown  Any ideas how   var      print        Would like to see  var  something else   3 print        Would print  something else

User · Answer

Technically the information is available to you, but as others have asked, how would you make use of it in a sensible way?

>>> x = 52
>>> globals()
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', 
'x': 52, '__doc__': None, '__package__': None}

This shows that the variable name is present as a string in the globals() dictionary.

>>> globals().keys()[2]
'x'

In this case it happens to be the third key, but there's no reliable way to know where a given variable name will end up

>>> for k in globals().keys():
...   if not k.startswith("_"):
...     print k
...
x
>>>

You could filter out system variables like this, but you're still going to get all of your own items. Just running that code above created another variable "k" that changed the position of "x" in the dict.

But maybe this is a useful start for you. If you tell us what you want this capability for, more helpful information could possibly be given.

User · Answer

It s not very Pythonesque but I was curious and found this solution  You need to duplicate the globals dictionary since its size will change as soon as you define a new variable   def var to name var         noinspection PyTypeChecker     dict vars   dict globals   items         var string   None      for name in dict vars keys            if dict vars name  is var              var string   name             break      return var string   if   name         main         test   3     print f test    test        print f variable name   var to name test       which returns   test   3 variable name  test

User · Answer

Totally possible with the python-varname package  python3   from varname import nameof  s    Hey    print  nameof s    Output  s  Get the package here  https   github com pwwang python-varname

User · Answer

You somehow have to refer to the variable you want to print the name of  So it would look like   print varname something else    There is no such function  but if there were it would be kind of pointless  You have to type out something else  so you can as well just type quotes to the left and right of it to print the name as a string   print  something else

User · Answer

I searched for this question because I wanted a Python program to print assignment statements for some of the variables in the program  For example  it might print  foo   3  bar   21  baz   432   The print function would need the variable names in string form  I could have provided my code with the strings  foo   bar   and  baz   but that felt like repeating myself  After reading the previous answers  I developed the solution below   The globals   function behaves like a dict with variable names  in the form of strings  as keys  I wanted to retrieve from globals   the key corresponding to the value of each variable  The method globals   items   returns a list of tuples  in each tuple the first item is the variable name  as a string  and the second is the variable value  My variablename   function searches through that list to find the variable name s  that corresponds to the value of the variable whose name I need in string form   The function itertools ifilter   does the search by testing each tuple in the globals   items   list with the function lambda x  var is globals   x 0    In that function x is the tuple being tested  x 0  is the variable name  as a string  and x 1  is the value  The lambda function tests whether the value of the tested variable is the same as the value of the variable passed to variablename    In fact  by using the is operator  the lambda function tests whether the name of the tested variable is bound to the exact same object as the variable passed to variablename    If so  the tuple passes the test and is returned by ifilter     The itertools ifilter   function actually returns an iterator which doesn t return any results until it is called properly  To get it called properly  I put it inside a list comprehension  tpl 0  for tpl     globals   items      The list comprehension saves only the variable name tpl 0   ignoring the variable value  The list that is created contains one or more names  as strings  that are bound to the value of the variable passed to variablename     In the uses of variablename   shown below  the desired string is returned as an element in a list  In many cases  it will be the only item in the list  If another variable name is assigned the same value  however  the list will be longer    gt  gt  gt  def variablename var           import itertools         return  tpl 0  for tpl in          itertools ifilter lambda x  var is x 1   globals   items           gt  gt  gt  var       gt  gt  gt  variablename var    var    gt  gt  gt  something else   3  gt  gt  gt  variablename something else    something else    gt  gt  gt  yet another   3  gt  gt  gt  variablename something else    yet another    something else

User · Answer

I d like to point out a use case for this that is not an anti-pattern  and there is no better way to do it  This seems to be a missing feature in python  There are a number of functions  like patch object  that take the name of a method or property to be patched or accessed  Consider this  patch object obj   quot method name quot   new reg  This can potentially start  quot false succeeding quot  when you change the name of a method   IE  you can ship a bug  you thought you were testing     simply because of a bad method name refactor  Now consider   varname   This could be an efficient  built-in function   But for now it can work by iterating an object or the caller s frame  Now your call can be  patch member obj  obj method name  new reg  And the patch function can call  varname var  obj obj  This would  assert that the var is bound to the obj and return the name of the member   Or if the obj is not specified  use the callers stack frame to derive it  etc  Could be made an efficient built in at some point  but here s a definition that works    I deliberately didn t support builtins  easy to add tho  Feel free to stick this in a package called varname py  and use it in your patch object calls  patch object obj  varname obj  obj method name   new reg  Note  this was written for python 3  import inspect  def  varname dict var  dct       key name   None     for key  val in dct items            if val is var              if key name is not None                  raise NotImplementedError  quot Duplicate names not supported  s   s quot     key name  key               key name   key     return key name  def  varname obj var  obj       key name   None     for key in dir obj           val   getattr obj  key          equal   val is var         if equal              if key name is not None                  raise NotImplementedError  quot Duplicate names not supported  s   s quot     key name  key               key name   key     return key name  def varname var  obj None       if obj is None          if hasattr var   quot   self   quot                return var   name           caller frame   inspect currentframe   f back         try              ret    varname dict var  caller frame f locals          except NameError              ret    varname dict var  caller frame f globals      else          ret    varname obj var  obj      if ret is None          raise NameError  quot Name not found   Note  builtins not supported  quot       return ret

User · Answer

I think this is a cool solution and I suppose the best you can get  But do you see any way to handle the ambigious results  your function may return  As  quot is quot  operator behaves unexpectedly with integers shows  low integers and strings of the same value get cached by python so that your variablename-function might priovide ambigous results with a high probability   In my case  I would like to create a decorator  that adds a  new variable to a class by the varialbename i pass it   def inject klass  dependency   klass   dict        variablename dependency   dependency   But if your method returns ambigous results  how can I know the name of the variable I added   var any var  myvarcontent  var myvar  myvarcontent   inject myvar  class myclasss        def myclass method self           print self   myvar     I can not be sure  that this variable will be set      Maybe if I will also check the local list I could at least remove the  dependency -Variable from the list  but this will not be a reliable result

User · Answer

By using the  the unpacking operator    gt  gt  gt  def tostr   kwargs       return kwargs   gt  gt  gt  var       gt  gt  gt  something else   3  gt  gt  gt  tostr var   var something else something else    var        something else  3

User · Answer

What are you trying to achieve  There is absolutely no reason to ever do what you describe  and there is likely a much better solution to the problem you re trying to solve    The most obvious alternative to what you request is a dictionary  For example    gt  gt  gt  my data     var    something    gt  gt  gt  my data  something else      something   gt  gt  gt  print my data keys     var    something else    gt  gt  gt  print my data  var   something   Mostly as a   challenge  I implemented your desired output  Do not use this code  please      usr bin env python2 6 class NewLocals         Please don t ever use this code          def   init   self  initial locals           self prev locals   list initial locals keys         def show new self  new locals           output        join list set new locals  - set self prev locals            self prev locals   list new locals keys            return output   Set up eww   None eww   NewLocals locals        Working  requested code  var       print eww show new locals       Outputs  var  something else   3 print eww show new locals      Outputs  something else    Further testing  another variable   4 and a final one   5  print eww show new locals      Outputs  another variable  and a final one

User · Answer

To get the variable name of var as a string  var   1000 var name    k for k v in locals   items   if v    var  0   print var name    --- gt  outputs  var

User · Answer

Does Django not do this when generating field names   http   docs djangoproject com en dev  topics db models  verbose-field-names  Seems reasonable to me

User · Answer

TL DR  Not possible  See  conclusion  at the end   There is an usage scenario where you might need this  I m not implying there are not better ways or achieving the same functionality  This would be useful in order to  dump  an arbitrary list of dictionaries in case of error  in debug modes and other similar situations  What would be needed  is the reverse of the eval   function  get indentifier name missing function    which would take an identifier name   variable   dictionary  etc  as an argument  and return a string containing the identifier   s name   Consider the following current state of affairs  random function argument data   If one is passing an identifier name   function   variable   dictionary  etc  argument data to a random function    another identifier name   one actually passes an identifier  e g    lt argument data object at 0xb1ce10 gt   to another identifier   e g    lt function random function at 0xafff78 gt     lt function random function at 0xafff78 gt   lt argument data object at 0xb1ce10 gt    From my understanding  only the memory address is passed to the function   lt function at 0xafff78 gt   lt object at 0xb1ce10 gt    Therefore  one would need to pass a string as an argument to random function   in order for that function to have the argument s identifier name  random function  argument data    Inside the random function   def random function first argument      one would use the already supplied string  argument data  to   serve as an  identifier name   to display  log  string split concat  whatever   feed the eval   function in order to get a reference to the actual identifier  and therefore  a reference to the real data  print  quot Currently working on quot   first argument  some internal var   eval first argument  print  quot here comes the data   quot    str some internal var      Unfortunately  this doesn t work in all cases  It only works if the random function   can resolve the  argument data  string to an actual identifier  I e  If argument data identifier name is available in the random function   s namespace  This isn t always the case    main1 py import some module1  argument data    my data   some module1 random function  argument data       some module1 py def random function first argument       print  quot Currently working on quot   first argument      some internal var   eval first argument      print  quot here comes the data   quot    str some internal var           Expected results would be  Currently working on  argument data here comes the data  my data  Because argument data identifier name is not available in the random function   s namespace  this would yield instead  Currently working on argument data Traceback  most recent call last     File  quot   main1 py quot   line 6  in  lt module gt      some module1 random function  argument data     File  quot   some module1 py quot   line 4  in random function     some internal var   eval first argument    File  quot  lt string gt  quot   line 1  in  lt module gt  NameError  name  argument data  is not defined   Now  consider the hypotetical usage of a get indentifier name missing function   which would behave as described above  Here s a dummy Python 3 0 code      main2 py import some module2 some dictionary 1            definition 1   text 1                                definition 2   text 2                                etc   etc     some other dictionary 2      key 3   value 3                                key 4   value 4                                 etc   etc         more such stuff   some other dictionary n      random n   random n                                etc   etc      for each one of my dictionaries in   some dictionary 1                                       some other dictionary 2                                                                                 some other dictionary n        some module2 some function each one of my dictionaries      some module2 py def some function a dictionary object       for  key   value in a dictionary object items            print  get indentifier name missing function a dictionary object                       quot      quot                   str  key                    quot       quot                   str  value            Expected results would be  some dictionary 1    definition 1     text 1 some dictionary 1    definition 2     text 2 some dictionary 1    etc     etc  some other dictionary 2    key 3     value 3 some other dictionary 2    key 4     value 4 some other dictionary 2    etc     etc                       some other dictionary n    random n     random n some other dictionary n    etc     etc   Unfortunately  get indentifier name missing function   would not see the  original  identifier names  some dictionary  some other dictionary 2 some other dictionary n   It would only see the a dictionary object identifier name  Therefore the real result would rather be  a dictionary object    definition 1     text 1 a dictionary object    definition 2     text 2 a dictionary object    etc     etc  a dictionary object    key 3     value 3 a dictionary object    key 4     value 4 a dictionary object    etc     etc                       a dictionary object    random n     random n a dictionary object    etc     etc   So  the reverse of the eval   function won t be that useful in this case   Currently  one would need to do this    main2 py same as above  except       for each one of my dictionaries names in    some dictionary 1                                                   some other dictionary 2                                                                                                         some other dictionary n             some module2 some function    each one of my dictionaries names                                        eval each one of my dictionaries names                      some module2 py     def some function a dictionary name object container           for  dictionary name   dictionary object in a dictionary name object container items                for  key   value in  dictionary object items                    print  str  dictionary name                            quot      quot                           str  key                            quot       quot                           str  value                 In conclusion   Python passes only memory addresses as arguments to functions  Strings representing the name of an identifier  can only be referenced back to the actual identifier by the eval   function if the name identifier is available in the current namespace  A hypothetical reverse of the eval   function  would not be useful in cases where the identifier name is not  seen  directly by the calling code  E g  inside any called function  Currently one needs to pass to a function   the string representing the identifier name the actual identifier  memory address     This can be achieved by passing both the  string  and eval  string   to the called function at the same time  I think this is the most  general  way of solving this egg-chicken problem across arbitrary functions  modules  namespaces  without using corner-case solutions  The only downside is the use of the eval   function which may easily lead to unsecured code  Care must be taken to not feed the eval   function with just about anything  especially unfiltered external-input data

User · Answer

print  var  print  something else    Or did you mean something else

User · Answer

I don t know it s right or not  but it worked for me def varname variable       names          for name in list globals   keys             string   f id  name            if id variable     eval string               names append name      return names 0

User · Answer

This is not possible   In Python  there really isn t any such thing as a  variable    What Python really has are  names  which can have objects bound to them   It makes no difference to the object what names  if any  it might be bound to   It might be bound to dozens of different names  or none   Consider this example   foo   1 bar   1 baz   1   Now  suppose you have the integer object with value 1  and you want to work backwards and find its name   What would you print   Three different names have that object bound to them  and all are equally valid   In Python  a name is a way to access an object  so there is no way to work with names directly   There might be some clever way to hack the Python bytecodes or something to get the value of the name  but that is at best a parlor trick   If you know you want print foo to print  foo   you might as well just execute print  foo  in the first place   EDIT  I have changed the wording slightly to make this more clear   Also  here is an even better example   foo   1 bar   foo baz   foo   In practice  Python reuses the same object for integers with common values like 0 or 1  so the first example should bind the same object to all three names   But this example is crystal clear  the same object is bound to foo  bar  and baz

User · Answer

This will work for simnple data types  str  int  float  list etc         def my print var str           print var str      globals   var str      a   5     b     hello     world        my print  a   a  5     my print  b   b    hello     world

User · Answer

as long as it s a variable and not a second class  this here works for me   def print var name variable    for name in globals         if eval name     variable          print name foo   123 print var name foo   gt  gt  gt foo   this happens for class members   class xyz       def   init   self            pass member   xyz   print var name member   gt  gt  gt member   ans this for classes  as example    abc   xyz print var name abc   gt  gt  gt abc  gt  gt  gt xyz   So for classes it gives you the name AND the properteries

User · Answer

Here is a succinct variation that lets you specify any directory  The issue with using directories to find anything is that multiple variables can have the same value  So this code returns a list of possible variables   def varname  var  dir locals       return   key for key  val in dir items   if id  val     id  var

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