Functions

Calling a function



In [1]:

    
x=5
y=7
z=max(x,y) #max is the function. x and y are the arguments
print(z) #print is the function. z is the argument

Installing libraries and importing functions



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!pip install easygui 
#pip: python installer program
# ! run the program from the shell (not from python)
# easygui: a python library for GUI widgets



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import easygui #Imports easygui into the current namespace. We now have access to functiona and objects in this library
easygui.msgbox("To be or not to be","What Hamlet elocuted") #msgbox is a function in easygui.









    



---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-2-3198e7a23cba> in <module>()
----> 1 import easygui #Imports easygui into the current namespace. We now have access to functiona and objects in this library
      2 easygui.msgbox("To be or not to be","What Hamlet elocuted") #msgbox is a function in easygui.

ImportError: No module named 'easygui'

Importing functions



In [3]:

    
import math #imports the math namespace into our program namespace
math.sqrt(34.23) #Functions in the math namespace have to be disambiguated









    Out[3]:





5.850640990524029



In [4]:

    
import math as m #imports the math namespace into our program namespace but gives it the name 'm'
m.sqrt(34.23) #Functions in the math namespace have to be disambiguated using the name 'm' rather than 'math'









    Out[4]:





5.850640990524029



In [ ]:



In [5]:

    
from math import sqrt #imports the sqrt function into our program namespace. No other math functions are accessible
sqrt(34.23) #No disambiguation necessary









    Out[5]:





5.850640990524029

Returning values from a function

The return statement tells a function what to return to the calling program



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def spam(x,y,k):
    if x>y:
        z=x
    else:
        z=y
    p = z/k
    return p #Only the value of p is returned by the function



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spam(6,4,2)









    Out[7]:





3.0

If no return statement, python returns None



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def eggs(x,y):
    z = x/y

print(eggs(4,2))









    



None

Returning multiple values



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def foo(x,y,z):
    if z=="DESCENDING":
        return max(x,y),min(x,y),z
    if z=="ASCENDING":
        return min(x,y),max(x,y),z
    else:
        return x,y,z



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a,b,c = foo(4,2,"ASCENDING")
print(a,b,c)









    



2 4 ASCENDING

Python unpacks the returned value into each of a,b, and c. If there is only one identifier on the LHS, it won't unpack



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a = foo(4,2,"ASCENDING")
print(a)









    



(2, 4, 'ASCENDING')

If there is a mismatch between the number of identifiers on the LHS and the number of values returned, you'll get an error



In [12]:

    
a,b = foo(4,2,"DESCENDING")









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-12-4bbd671daaf6> in <module>()
----> 1 a,b = foo(4,2,"DESCENDING")

ValueError: too many values to unpack (expected 2)

Value assignment to arguments

Left to right

Unless explicitly assigned to the argument identifiers in the function definition



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def bar(x,y):
    return x/y
bar(4,2) #x takes the value 4 and y takes the value 2



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def bar(x,y):
    return x/y
bar(y=4,x=2) #x takes the value 2 and y takes the value 4 (Explicit assignment)









    Out[13]:





0.5

A function can have function arguments



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def order_by(a,b,order_function):
    return order_function(a,b)

print(order_by(4,2,min))
print(order_by(4,2,max))

2
4



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def change(x):
    x = (1,)
    print(x)
x = (1, 2)
change(x)
print(x)









    



(1,)
(1, 2)



In [26]:

    
def replace(test_string, replace_string):
    start_index = test_string.find(replace_string)
    result = ""
    x = "bodega"
    if start_index >= 0:
        result = test_string[start_index:start_index+len(replace_string)]
        result = test_string.replace(result,x)
    return result
    
print(replace("Hi how are you?", "yu"))



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