dicto = {12:{34:45,56:78},45:{67:23,90:15}}

dicto = {12:{34:45,56:78},45:{67:23,90:15}}
for k,v in dicto.items():
    for i in v.keys():
        if i == 67:
            del v[i]

print(dicto)

Traceback (most recent call last):
  File "/home/souvik/Sublime-text programs/TestCode.py", line 4, in <module>
    for i in v.keys():
RuntimeError: dictionary changed size during iteration
[Finished in 0.1s with exit code 1]