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Functions, Parameters, and Globals
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<<Function Definition II func3.py Polynomial Evaluator>>
#!/usr/bin/python3

# References inside functions are local...
snoggle = 17
def wongle(n):
    snoggle = n

print('A:', snoggle,end=' ')
wongle(235)
print(snoggle)

# ...unless declared global.
def wangle(n):
    global snoggle
    snoggle = n

print('B:', snoggle,end=' ')
wangle(235)
print(snoggle)

# Arguments are pass-by-value...
def snapple(n):
    n = 55

print('C:', snoggle,end=' ')
wangle(snoggle)
print(snoggle)

# ...except for the contents objects, such as lists...
def snarffle(z):
    z.append(22)

toggle = [ 'a', 'b', 'c' ];
print('D:', toggle,end=' ')
snarffle(toggle)
print(toggle)

# ...which means the contents of the object, not the parameter.
def snarggle(z):
    z = [ 4, 5 ]

print('F:', toggle,end=' ')
snarggle(toggle)
print(toggle)
Argument passing in Python is a lot like Java. Arguments are passed by value, so that changing a parameter does not change the value at the caller. However, objects (including built-in types which are represented as objects) are passed as references, so using the the paramater to change them will make changes visible to the caller.
<<Function Definition II Polynomial Evaluator>>