[Python] Using dictionary inside a function

I found an exercise in a Udemy's Python course which asks me to create a function called return_day. It suggests me to use a dictionary, but I have been trying for the past two hours without success. So I passed the exercise writing:

def return_day(x):
if x == 1:
return "Sunday"
elif x==2:
return "Monday"
elif x==3:
return "Tuesday"
elif x==4:
return "Wednesday"
elif x==5:
return "Thursday"
elif x==6:
return "Friday"
elif x==7:
return "Saturday"
return None


...but it's completely different. Could someone help me? Why the code below does not work?

def return_day(x):
if x > 0 and x<=7:
return x=dict(1="Sunday",2="Monday",3="Tuesday",4="Wednesday",5="Thursday",6="Friday",7="Saturday")

return None

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