Getting error while popping in dictionary python

Question

I have a dictionary

price={'10MAR23': 113.49999999999999,
 '3MAR23': 19.10000000000001,
 '25FEB23': 19.100000000000012,
 '28APR23': 3.5,
 '26FEB23': 0.4,
 '31MAR23': 27.5,
 '17MAR23': 3.1}

I want to replace the keys with respective dates with format as %d%m%y like

The following code does that,

for i in price:
        new_key=datetime.datetime.strptime(i,'%d%b%y').strftime('%d%m%y')
        price[new_key]=price.pop(i)

but getting error like

ValueError: time data '030323' does not match format '%d%b%y'

Asked By: Madan

||

Source

Answer 1

This happens because you are looping over price while modifying its keys at the same time. You can avoid that by copying the dictionary before performing the loop, with for i in dict(price):, as so:

price = {'10MAR23': 113.49999999999999,
         '3MAR23': 19.10000000000001,
         '25FEB23': 19.100000000000012,
         '28APR23': 3.5,
         '26FEB23': 0.4,
         '31MAR23': 27.5,
         '17MAR23': 3.1}

for i in dict(price):
    new_key = datetime.datetime.strptime(i,'%d%b%y').strftime('%d%m%y')
    price[new_key] = price.pop(i)

Alternatively, you can create a new dictionary from the old one with a dictionary comprehension

price = {datetime.datetime.strptime(k, '%d%b%y').strftime('%d%m%y'): v 
         for k, v in price.items()}

Answered By: oskros

Answer 2

The error you are getting is because you are trying to change the keys of a dictionary while iterating over it. This modifies the size of the dictionary and causes an inconsistency in the loop.

One way to avoid this error is to create a copy of the original dictionary and iterate over that instead. Then you can use the pop() function to remove the old key and add the new key with the same value. For example:

price_copy = price.copy() for i in price_copy: new_key=datetime.datetime.strptime(i,‘%d%b%y’).strftime(‘%d%m%y’) price[new_key]=price.pop(i)

Another way is to use a dictionary comprehension to create a new dictionary with the updated keys. For example:

price = {datetime.datetime.strptime(i,‘%d%b%y’).strftime(‘%d%m%y’): v for i, v in price.items()}

Answered By: Shoaib

Getting error while popping in dictionary python

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