trjhtr

Task:

The task requires creating a class (say, ConfigDict) which inherits from the dict class.

It is supposed to save its keys and values in a file.
If a file does not exist, the instance of ConfigDict should be able to create it.

Examples:

For instance, the following code:

fh=open("config.txt","w")
fh.write("key1 = 5n")
fh.write("key2 = 3n")
fh.close()
cd=ConfigDict("config.txt")
cd.items()

would generate an output dict_items([('key1', '5'), ('key2', '3')]).

If a file does not exists, it should be possible for the instance to create it and save its data inside it.

dd=ConfigDict("test.txt")
dd["keyA"] = 'testA'
dd["keyB"] = 'testB'
dd.items()

The above lines would produce dict_items([('keyA', 'testA'), ('keyB', 'testB')]) (and a print message).

My attempt:

I will greatly appreciate any comments.

class ConfigDict(dict):
 def __init__(self,file):
 self.file = file

 try: #check if file exists
 with open(self.file,"r+") as fh:
 for line in fh:
 key, item = line.replace(" ", "").rstrip().split("=")
 dict.__setitem__(self,key,item)

 except: 
 print("creating "+file)
 fh=open(self.file,"w")
 fh.close()


 def __setitem__(self,key,item):
 dict.__setitem__(self,key,item) #to avoid infinite loop
 lines = open(self.file).read().splitlines()

 for index, line in enumerate(lines):
 if line.replace(" ", "").rstrip().split("=")[0] == key:
 lines[index] = str(key)+" = "+str(item)
 else:
 lines.append(str(key)+" = "+str(item))

 open(self.file,'w').write('n'.join(lines))

Corrected version

import os

class ConfigDict(dict):
 def __init__(self,file):
 self.file = file
 if os.path.isfile(self.file):
 with open(self.file,"r") as fh:
 for line in fh:
 key, item = line.replace(" ", "").rstrip().split("=")
 dict.__setitem__(self,key,item)

 def __setitem__(self,key,item):
 dict.__setitem__(self,key,item) 
 with open(self.file, 'w') as save_file:
 for key, value in self.items():
 save_file.write(" = n".format(key, value))

bugs:

1. Your implementation of __setitem__() does not to add a line
   if the key does not exist in the file yet.

other issues:

1. There is no need to create the file if it does not exist in
   __init__(), as open(..., 'w') in __setattr__() will create
   it for you.




2. It is gennerally not a good idea to print from a data class
   (i.e. print("creating "+file)) as this makes the class unuseable for
   programs that use stdout.



3. 
   

   Iterating over a file in python automatically splits on lines so

   
   
   

   lines = open(self.file).read().splitlines()
   for index, line in enumerate(lines):
   

   
   
   

   could be written as

   
   
   

   for index, line in enumerate(open(self.file)):
   

   
   
   

   (like you did in __init__())

   
   


4. 
   

   If you are going to completly rewrite the file on every
   __setitem__(), there is no point in reading the file first, as this
   takes more time and is harder to read. here is an example
   __setitem__():

   
   
   

   def __setitem__(self,key,item):
    dict.__setitem__(self,key,item) #to avoid infinite loop
   
    with open(self.file, 'w') as save_file:
    for key, value in self.items():
    save_file.write(" = n".format(key, value))