CS1010S Tutorial 2 HOF Example

gistfile1.py

def bank_account(balance):
    # Inner functions are created in the scope of the
    # outer function, and as such have 'knowledge' of
    # the scope.
    #
    # In this case, it knows about the balance.
    # This function returns a string telling us
    # whether the owner is rich or poor
    def are_you_rich():
        # The inner function can access/read the variables
        # defined in the outer scope, but it *cannot*
        # modify it (Sorry!)
        if balance > 1000:
            return "rich!"
        else:
            return "poor :("

    # Returns the are_you_rich *function*
    # that has bounded to the current scope
    return are_you_rich

######
# Test
######

my_account = bank_account(50)
your_account = bank_account(5000)

# Now my_account and your_account are *functions*,
# so you have to invoke them to get the output

print("I am", my_account())         # Out: I am poor ;(
print("You are", your_account())    # Out: You are rich!

# Let's see what my_account and your_account are:
print(my_account)                   # <function bank_account.<locals>.are_you_rich at 0x1079e2b90>
print(your_account)                 # <function bank_account.<locals>.are_you_rich at 0x107a05b90>

# The last number (address) might be different from what I've got, but its not important. The important thing
# is the address is different for my_account and your_account.
# It also shows you where the function is defined

The inner function can modify the variables

    # defined in the outer scope, but it *cannot*
    # modify it

should be the inner function can 'access' the variables defined in the outer scope, but it cannot modify it

isn't it?

thanks for the explanation, I think I've formulated a good explanation, will email you to see if its suitable to share with the rest. :D

Ah yes, that is correct! I can't believe I've made that mistake lol.

Sure! I'll be happy to take a look at that :)