Using a for loop and if statement in Python

Question

I am trying to solve a problem similar to this one below:

You are provided with a dictionary, for loop through all the values in the dictionary and check if they are equal to 45. If they are, delete them from the list. Below is the dictionary:

this_dict = {
 "dogs val":45, "sheep val":475, "cats val":33, "fish val":425, "crab val":11, "monkey val":45, "shark val":45,
 "badger val":45,"octopus val":55,"cheetah val":45,"owl val":656

I am then hoping to print and output the dictionary provided, but with all the key:value pairs with a value of 45 removed.

This is what I have tried thus far:

for i in this_dict:
 if this_dict[i] == 45:
 del this_dict[i]

• Caridorc: What is the output that you get vs the expected output?
• Caridorc: Try making the title of the post more descriptive of your problem

Answer 1

Why not filter in a dict comprehension ?

Rather than deleting in original dict, you create a new one and can reassign to your original dict variable.

{k: v for k, v in this_dict.items() if v != 45}

gives

{'sheep val': 475,
 'cats val': 33,
 'fish val': 425,
 'crab val': 11,
 'octopus val': 55,
 'owl val': 656}

---

Full demo

this_dict = {
 "dogs val": 45,
 "sheep val": 475,
 "cats val": 33,
 "fish val": 425,
 "crab val": 11,
 "monkey val": 45,
 "shark val": 45,
 "badger val": 45,
 "octopus val": 55,
 "cheetah val": 45,
 "owl val":656
}
id(this_dict) # 4478365376
this_dict = {k: v for k, v in this_dict.items() if v != 45}
id(this_dict) # 4474822144 different id, it's a new dict

Answer 2

I guess you got a RuntimeError because you iterate on the dictionary which changes. If you create a list with the keys of the dict, you do not have this problem:

this_dict = {"dogs val":45, "sheep val":475, "cats val":33, "fish val":425, "crab val":11, "monkey val":45, "shark val":45, "badger val":45,"octopus val":55,"cheetah val":45,"owl val":656}
for i in list(this_dict.keys()):
 if this_dict[i] == 45:
 del this_dict[i]

Answer 3

Your code did not work because you cannot modify the same dictionary you are iterating on. You receive that error:

RuntimeError: dictionary changed size during iteration

You can solve it using list, that make a copy of the dictionary:

for key in list(this_dict):
 if this_dict[key] == 45:
 del this_dict[key]

It would be a much more pythonic solution to use a dict comprehension, but using for loops was a requirement in the question.

Answer 4

You should try the following:

for key in this_dict.keys():
 if this_dict[key] == 45:
 del this_dict[key]

Let me know if you have any questions.

• ljmc: Why get val out to use this_dict[key] ?