[Python] TypeError: keys() takes no arguments (1 given)

When I hit "5", my program doesn't give me back all the keys in a form of a list (as expected) but an error occurs instead:

TypeError: keys() takes no arguments (1 given)
​

Why is that?

elif choice == "5":
print("\nOto wszystkie terminy znajdujace sie w slowniku:")
for i in dictionary:
print(dictionary.keys(i))

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