Python: Inserting into dictionary using FOR Loop

Question

i have searched through the forum and can't understand if i can use the following construct to insert new entries into my Python Dictionary...without turning it into a list.

for x in range(3):    
   pupils_dictionary = {}
   new_key =input('Enter new key: ')
   new_age = input('Enter new age: ')
   pupils_dictionary[new_key] = new_age
print(pupils_dictionary)

The output is as follows:

Enter new key: Tim
Enter new age: 45
Enter new key: Sue
Enter new age: 16
Enter new key: Mary
Enter new age: 15
{'Mary': '15'}

Why does ONLY Mary:15 go in, and none of the others?

thanks/

Important thing to consider: what do you do when the user re-enters the same name?! Dictionaries can't have duplicate keys -- this is possibly better as a list of tuples. — Adam Smith, Mar 11 '14 at 23:55
@user3396486 I rollbacked your edit since all of the answers here were posted based on your example (which you removed with your edit) — Steinar Lima, Mar 12 '14 at 00:17

score 10 · Accepted Answer · answered Mar 12 '14 at 00:03

10

Its because you do pupils_dictionary = {}

Inside your loop, on every loop, its value get reset to {}

suggestion :

use raw_input instead of input

so this code should work :

pupils_dictionary = {}

for x in range(3):    
    new_key = raw_input('Enter new key: ')
    new_age = raw_input('Enter new age: ')
    pupils_dictionary[new_key] = new_age
print(pupils_dictionary)

answered Mar 12 '14 at 00:03

Frederic Nault

986
9
14

1

`input` replaces `raw_input` in Python 3.x – jonrsharpe Mar 12 '14 at 00:05

score 6 · Answer 2 · answered Mar 11 '14 at 23:52

You create the dictionary anew with each loop:

for x in range(3):    
   pupils_dictionary = {}
   new_key =input('Enter new key: ')
   ...

Instead, create it once outside the loop:

pupils_dictionary = {}
for x in range(3):    
   new_key =input('Enter new key: ')
   ...

score 1 · Answer 3 · answered Mar 11 '14 at 23:53

You redefine the dictionary as empty during every pass through the loop. The code should be.

pupils_dictionary = {}
for x in range(3):    
  new_key =input('Enter new key: ')
  new_age = input('Enter new age: ')
  pupils_dictionary[new_key] = new_age
  print(pupils_dictionary)

Python: Inserting into dictionary using FOR Loop

3 Answers3

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