RuntimeError: dictionary changed size during iteration PYTHON

Question

I'm trying to remove a key-value from a dictionary by a condition, but when i try i recive the error

RuntimeError: dictionary changed size during iteration

Here is my code

threading.Timer(5.0, compare_time_connecteds).start()   

FMT = '%H:%M:%S'                                                
datesys_compare = datetime.now().strftime("%H:%M:%S")     

keys = connecteds.keys()

if len(keys) != 0:
    for i in keys:                   
        true_time = datetime.strptime(datesys_compare, FMT) - datetime.strptime(connecteds.get(i), FMT)    
        difference_in_seconds = true_time.total_seconds()                                   #       

        if difference_in_seconds > 20:               
            connecteds.pop(i)

And here is the error

 for i in keys:      
 RuntimeError: dictionary changed size during iteration

I solved this forcing the keys to be a list

FMT = '%H:%M:%S'                                                
datesys_compare = datetime.now().strftime("%H:%M:%S")     

keys = list(connecteds.keys())

Size changing your dictionary while looping it is problematic. Try adding keys and values to an empty dict unless difference_in_seconds > 20 — Oliver Mohr Bonometti
– Oliver Mohr Bonometti, Commented Apr 6, 2022 at 20:00
Just force the keys to be a list and not keys object, to do so: keys = list(connecteds.keys()). This happens because the keys object you are iterating over is taking values from the respective dictionary in "real time" and not a static list. — Elger
– Elger, Commented Apr 6, 2022 at 20:01
@Elger thanks so much for your help! This list solve my problem! — Guilherme Londero
– Guilherme Londero, Commented Apr 6, 2022 at 20:07

damaBeugXam · Accepted Answer · 2022-04-06 20:00:49Z

1

Try replacing the variable keys by the expression connecteds.keys(). I am assuming that you are using Threads and also that connecteds is being used in these threads. May be that is changing the size.

answered Apr 6, 2022 at 20:00

damaBeugXam

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