Getting the name of a variable as a string

Question

This thread discusses how to get the name of a function as a string in Python  How to get a function name as a string  How can I do the same for a variable  As opposed to functions  Python variables do not have the   name   attribute  In other words  if I have a variable such as  foo   dict   foo  bar     2  I am looking for a function attribute  e g  retrieve name   in order to create a DataFrame in Pandas from this list  where the column names are given by the names of the actual dictionaries    List of dictionaries for my DataFrame list of dicts    n jobs  users  queues  priorities  columns    retrieve name d  for d in list of dicts

User · Answer

just another way to do this based on the content of input variable:

(it returns the name of the first variable that matches to the input variable, otherwise None. One can modify it to get all variable names which are having the same content as input variable)

def retrieve_name(x, Vars=vars()):
    for k in Vars:
        if type(x) == type(Vars[k]):
            if x is Vars[k]:
                return k
    return None

User · Answer

gt  gt  my var   5  gt  gt  my var name     k for k v in locals   items   if v    my var  0   gt  gt  my var name   my var   In case you get an error if myvar points to another variable  try this  suggested by  mherzog -   gt  gt  my var   5  gt  gt  my var name     k for k v in locals   items   if v is my var  0   gt  gt  my var name   my var   locals   - Return a dictionary containing the current scope s local variables  by iterating through this dictionary we can check the key which has a value equal to the defined variable  just extracting the key will give us the text of variable in string format  from  after a bit changes  https   www tutorialspoint com How-to-get-a-variable-name-as-a-string-in-Python

User · Answer

I try to get name from inspect locals  but it cann t process var likes a 1   b val  After it  I got a new idea --- get var name from the code  and I try it succ  code like below     direct get from called function code def retrieve name ex var       stacks   inspect stack       try          func   stacks 0  function         code   stacks 1  code context 0          s   code index func          s   code index      s   len func     1         e   code index      s          return code s e  strip       except          return

User · Answer

For constants  you can use an enum  which supports retrieving its name

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On python3  this function will get the outer most name in the stack   import inspect   def retrieve name var                       Gets the name of var  Does it from the out most frame inner-wards           param var  variable to get name from           return  string                     for fi in reversed inspect stack                 names    var name for var name  var val in fi frame f locals items   if var val is var              if len names   gt  0                  return names 0    It is useful anywhere on the code  Traverses the reversed stack looking for the first match

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Maybe this could be useful   def Retriever bar       return  list globals   keys     list map lambda x  id x   list globals   values      index id bar      The function goes through the list of IDs of values from the global scope  the namespace could be edited   finds the index of the wanted required var or function based on its ID  and then returns the name from the list of global names based on the acquired index

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If the goal is to help you keep track of your variables  you can write a simple function that labels the variable and returns its value and type  For example  suppose i f 3 01 and you round it to an integer called i n to use in a code  and then need a string i s  that will go into a report    def whatis string  x       print string   value   repr x  type x       return string   value   repr x  repr type x   i f 3 01 i n int i f  i s str i n  i l  i f  i n  i s  i u  i f  i n  i s      make report that identifies all types report   n  20       nThis is the report  n  report   whatis  i f   i f    n  report  whatis  i n   i n    n  report  whatis  i s   i s    n  report  whatis  i l   i l    n  report  whatis  i u   i u    n  print report    This prints to the window at each call for debugging purposes and also yields a string for the written report   The only downside is that you have to type the variable twice each time you call the function   I am a Python newbie and found this very useful way to log my efforts as I program and try to cope with all the objects in Python   One flaw is that whatis   fails if it calls a function described outside the procedure where it is used   For example  int i f  was a valid function call only because the int function is known to Python   You could call whatis   using int i f  2   but if for some strange reason you choose to define a function called int squared it must be declared inside the procedure where whatis   is used

User · Answer

I wrote the package sorcery to do this kind of magic robustly  You can write   from sorcery import dict of  columns   dict of n jobs  users  queues  priorities    and pass that to the dataframe constructor  It s equivalent to   columns   dict n jobs n jobs  users users  queues queues  priorities priorities

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Whenever I have to do it  mostly while communicating json schema and constants with the frontend I define a class as follows class Param      def   init   self  name  value           self name   name         self value   value  Then define the variable with name and value  frame folder count   Param   name   frame folder count    value  10    Now you can access the name and value using the object   gt  gt  gt  frame folder count name  frame folder count

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gt  gt  gt  locals    foo       gt  gt  gt  globals    foo        If you wanted to write your own function  it could be done such that you could check for a variable defined in locals then check globals  If nothing is found you could compare on id   to see if the variable points to the same location in memory   If your variable is in a class  you could use className dict keys   or vars self  to see if your variable has been defined

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Even if variable values don t point back to the name  you have access to the list of every assigned variable and its value  so I m astounded that only one person suggested looping through there to look for your var name    Someone mentioned on that answer that you might have to walk the stack and check everyone s locals and globals to find foo  but if foo is assigned in the scope where you re calling this retrieve name function  you can use inspect s current frame to get you all of those local variables   My explanation might be a little bit too wordy  maybe I should ve used a  foo  less words   but here s how it would look in code  Note that if there is more than one variable assigned to the same value  you will get both of those variable names    import inspect  x y z   1 2 3  def retrieve name var       callers local vars   inspect currentframe   f back f locals items       return  var name for var name  var val in callers local vars if var val is var   print retrieve name y      If you re calling this function from another function  something like   def foo bar       return retrieve name bar   foo baz    And you want the baz instead of bar  you ll just need to go back a scope further  This can be done by adding an extra  f back in the caller local vars initialization   See an example here  ideone

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def name   variables       return  x for x in variables    It s used like this   name variable variable

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I don t believe this is possible  Consider the following example    gt  gt  gt  a       gt  gt  gt  b   a  gt  gt  gt  id a  140031712435664  gt  gt  gt  id b  140031712435664   The a and b point to the same object  but the object can t know what variables point to it

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from varname import nameof  s    Hey    print  nameof s    Output  s  Package  https   github com pwwang python-varname

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Following method will not return the name of variable but using this method you can create data frame easily if variable is available in global scope   class CustomDict dict       def   add   self  other           return CustomDict    self    other    class GlobalBase type       def   getattr   cls  key           return CustomDict  key  globals   key         def   getitem   cls  keys           return CustomDict  key  globals   key  for key in keys    class G metaclass GlobalBase       pass  x  y  z   0  1  2  print  method 1    G  x    y    z      Outcome  method 1    x   0   y   1   z   2  print  method 2    G x   G y   G z    Outcome  method 2    x   0   y   1   z   2   A    0  1  B    1  2  pd DataFrame G A   G B    It will return a data frame with A and B columns

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With Python 3 8 one can simply use f-string debugging feature   gt  gt  gt  foo   dict    gt  gt  gt  f  foo    split      0   foo

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In Python  the def and class keywords will bind a specific name to the object they define  function or class   Similarly  modules are given a name by virtue of being called something specific in the filesystem  In all three cases  there s an obvious way to assign a  canonical  name to the object in question   However  for other kinds of objects  such a canonical name may simply not exist  For example  consider the elements of a list  The elements in the list are not individually named  and it is entirely possible that the only way to refer to them in a program is by using list indices on the containing list  If such a list of objects was passed into your function  you could not possibly assign meaningful identifiers to the values   Python doesn t save the name on the left hand side of an assignment into the assigned object because    It would require figuring out which name was  canonical  among multiple conflicting objects  It would make no sense for objects which are never assigned to an explicit variable name  It would be extremely inefficient  Literally no other language in existence does that    So  for example  functions defined using lambda will always have the  name   lt lambda gt   rather than a specific function name   The best approach would be simply to ask the caller to pass in an  optional  list of names  If typing the             is too cumbersome  you could accept e g  a single string containing a comma-separated list of names  like namedtuple does

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You can try the following to retrieve the name of a function you defined  does not work for built-in functions though    import re def retrieve name func       return re match   lt function s   w   s at     str func   group 1   def foo x       return x  2  print retrieve name foo     foo

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Many of the answers return just one variable name  But that won t work well if more than one variable have the same value  Here s a variation of Amr Sharaki s answer which returns multiple results if more variables have the same value  def getVariableNames variable       results          globalVariables globals   copy       for globalVariable in globalVariables          if id variable     id globalVariables globalVariable                results append globalVariable      return results  a   1 b   1 getVariableNames a      a    b

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Using the python-varname package  you can easily retrieve the name of the variables https   github com pwwang python-varname As of v0 6 0  in your case  you can do  from varname helpers import Wrapper  foo   Wrapper dict       foo name     foo    foo value       foo value  bar     2  For list comprehension part  you can do  n jobs   Wrapper  lt original value gt    users   Wrapper  lt original value gt    queues   Wrapper  lt original value gt    priorities   Wrapper  lt original value gt     list of dicts    n jobs  users  queues  priorities  columns    d name for d in list of dicts      n jobs    users    queues    priorities     REMEMBER that you have to access the  lt original value gt  by d value  You can also try to retrieve the variable name DIRECTLY  from varname import nameof  foo   dict    fooname   nameof foo    fooname     foo   Note that this is working in this case as you expected  n jobs    lt original value gt  d   n jobs  nameof d    will return d  instead of n jobs   nameof only works directly with the variable  I am the author of this package  Please let me know if you have any questions or you can submit issues on Github

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The only objects in Python that have canonical names are modules  functions  and classes  and of course there is no guarantee that this canonical name has any meaning in any namespace after the function or class has been defined or the module imported  These names can also be modified after the objects are created so they may not always be particularly trustworthy   What you want to do is not possible without recursively walking the tree of named objects  a name is a one-way reference to an object  A common or garden-variety Python object contains no references to its names  Imagine if every integer  every dict  every list  every Boolean needed to maintain a list of strings that represented names that referred to it  It would be an implementation nightmare  with little benefit to the programmer

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I have a method  and while not the most efficient   it works   and it doesn t involve any fancy modules    Basically it compares your Variable s ID to globals   Variables  IDs  then returns the match s name   def getVariableName variable  globalVariables globals   copy             Get Variable Name as String by comparing its ID to globals   Variables  IDs          args              variable var   Variable to find name for  Obviously this variable has to exist           kwargs              globalVariables dict   Copy of the globals   dict  Adding to Kwargs allows this function to work properly when imported from another  py              for globalVariable in globalVariables          if id variable     id globalVariables globalVariable      If our Variable s ID matches this Global Variable s ID                return globalVariable   Return its name from the Globals   dict

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This function will print variable name with its value  import inspect  def print this var       callers local vars   inspect currentframe   f back f locals items       print str  k for k  v in callers local vars if v is var  0        str var        Input  amp  Function call     my var   10  print this my var      Output     my var  10

User · Answer

Here s one approach  I wouldn t recommend this for anything important  because it ll be quite brittle  But it can be done   Create a function that uses the inspect module to find the source code that called it  Then you can parse the source code to identify the variable names that you want to retrieve  For example  here s a function called autodict that takes a list of variables and returns a dictionary mapping variable names to their values  E g    x    foo  y    bar  d   autodict x  y  print d   Would give     x    foo    y    bar     Inspecting the source code itself is better than searching through the locals   or globals   because the latter approach doesn t tell you which of the variables are the ones you want   At any rate  here s the code   def autodict  args       get rid of     autodict                n       calling code   inspect getouterframes inspect currentframe    1  4  0      calling code   calling code calling code index  autodict         for garbage in get rid of          calling code   calling code replace garbage          var names  var values   calling code split    args     dyn dict    var name  var value for var name  var value in                 zip var names  var values       return dyn dict   The action happens in the line with inspect getouterframes  which returns the string within the code that called autodict   The obvious downside to this sort of magic is that it makes assumptions about how the source code is structured  And of course  it won t work at all if it s run inside the interpreter

User · Answer

I think it s so difficult to do this in Python because of the simple fact that you never will not know the name of the variable you re using  So  in his example  you could do   Instead of   list of dicts    n jobs  users  queues  priorities   dict of dicts     n jobs    n jobs   users    users   queues    queues   priorities    priorities

[python] Getting the name of a variable as a string

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