Python: How to create for loop that change dict value and append it to the list?

Question

i tried to create a for loop that can change the value of dictionary 'title'. The new value will be then appended to the b list. So there will be 5 dict in b list with different 'title' value. This is my code.

dictionary = {'title': 'hello', 'black': 'white', 'yellow':'green'}
b = []
for a in range(5):
    dictionary['title'] = str(a)
    b.append(dictionary)
print b

The result is:

[{'black': 'white', 'yellow': 'green', 'title': '4'}, {'black': 'white', 'yellow': 'green', 'title': '4'}, {'black': 'white', 'yellow': 'green', 'title': '4'}, {'black': 'white', 'yellow': 'green', 'title': '4'}, {'black': 'white', 'yellow': 'green', 'title': '4'}]

[Finished in 0.136s]

Why all of the 'title' have the same value? How can I get a different number for each dicts appended to the list. Thanks

Just use a print b inside the loop, You will understand everything. — Rahul K P
– Rahul K P, Commented May 9, 2017 at 14:26

Uriel · Accepted Answer · 2017-05-09 14:24:53Z

3

When you are appending dictionary, you are actually appending its reference since dictionaries are mutable - that's why all of the entries are actually pointing to a single copy of the dictionary. Use it's copy method to append a copy of it instead of the original:

b.append(dictionary.copy())

answered May 9, 2017 at 14:24

Uriel

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1 Comment

jted95 Over a year ago

thank you very much, I didn't know that it is mutable.

Scott Hunter · Accepted Answer · 2017-05-09 14:24:57Z

0

You keep appending the same dictionary (note that they don't all just have the same value, but the last value that element was set to); if you want them to be different, you have to make a new dictionary for each appending.

answered May 9, 2017 at 14:24

Scott Hunter

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