python - Need help understanding how this recursive function is working -

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Here is a function (credit to user abot, to provide it in another question) 

  Diff Transgress (FTP): level = {} entry (for path in path) in ftp.nlst () if the path is not ('.', '..')): ftp.cwd (entry) Level [entry] = reverse level

This is what I do not understand: When the python enters the function, it creates an empty dictionary ( level ). For loop, it stores a directory name in the dictionary as a key, for the value of that key, the dragon enters the function again and searches for a directory and it becomes the value of that key .

But, how do you remember the values ​​within the levels? I mean, it should not be reset / empty every time Pygm enters the function?

Each "instance" of the function has its own copy of level and There is no side effect between different codes of level .

Take this folder tree: 

  root `-home | - lyrae | | - ftp.py | When you call  ftp  to  Route  then : 
  : 
 
 
 
 <<> 
  •   FTP (root)  creates a blank  level  
  •   ftp ( Root)  Calculates the subfolders  (home) . 
    •  
  •   FTP (root)  first selects the subfolder and changes the directory in it. 
    •  
  •   set  level [home]  for the result of  ftp  in the current folder. 
    •   
     
       
    •   FTP (Home)  creates an empty  level  dictionary 
      •  
    •   Ftp (home)  subfolders enumerates:  
    •   FTP (Home)  first selects the subfolder and changes the directory in it. 
      •  
    •   ftp        
         
            <      FTP (Lira)  creates a blank  level  dictionary  
        •   FP (Lira)  calculates subfolders:  () . 
          •  
        •   ftp (lyrae)  is out of the subfolder for parsing and return  level . 
          •  
        •   ftp (home)  completes the assignment:  level = {'lyrae': {}}  
          •  
        •   FTP (home)  changes to the next folder. 
          •  
        •   FTP (home)  set  level [badp]  for the result of  ftp  in the current code. 
          •  
         
         
           
        •   ftp (<< Code> level  
        •   ftp (badp)  calculates the subfolder :  () .  / li> 
        •   FTP (badp) is out of the subfolder for the pars and return  level . 
          •  
        •  > completes the FTP (home)  assignment:  level = {'lirai': {}, 'badp': { }}  
          •  
        •    level  
          •  
          
           
        •   FTP    is out of the subfolder for parsing and returning  assigns Nt:  level = {'home': {'lyrae': {}, 'badp ': {}}}  
          •  
        •   ftp (root)   level  is out of the subfolder for parsing and returning. 
          •

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