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Subprograms: functions and procedures
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Subprograms are named blocks of code you can call whenever you need them. They are how big programs stay organised.
Functions and procedures
A function returns a value with return.
def area(width, height):
return width * height
print(area(4, 5))
A procedure carries out a task but does not return a value.
def greet(name):
print("Hello", name)
greet("Kai")
Parameters are the names in the brackets (width, height). The values passed in when it is called (4, 5) are the arguments.
def area(width, height):
return width * height
print(area(4, 5))
A procedure carries out a task but does not return a value.
def greet(name):
print("Hello", name)
greet("Kai")
Parameters are the names in the brackets (width, height). The values passed in when it is called (4, 5) are the arguments.
Built-in and library subprograms
Python has built-in subprograms such as print(), len(), int() and input().
Library subprograms are imported, for example:
import random
dice = random.randint(1, 6) gives a whole number from 1 to 6 inclusive.
Library subprograms are imported, for example:
import random
dice = random.randint(1, 6) gives a whole number from 1 to 6 inclusive.
Local and global variables
A local variable is created inside a subprogram and only exists while it runs.
A global variable is created in the main program and can be read anywhere.
Using local variables avoids one part of a program accidentally changing another.
Benefits of subprograms: code is reused instead of repeated, each part can be tested on its own, programs are easier to read, and work can be shared in a team.
A global variable is created in the main program and can be read anywhere.
Using local variables avoids one part of a program accidentally changing another.
Benefits of subprograms: code is reused instead of repeated, each part can be tested on its own, programs are easier to read, and work can be shared in a team.
What does this print?
x = 10
def change():
x = 5
return x
y = change()
print(x + y)
- x = 5 inside change() is a new local variable.
- The global x is still 10, and y = 5.
- 10 + 5
Answer: 15
Functions return values; procedures do not. Parameters receive values passed in. Local variables exist only inside the subprogram. Subprograms make code reusable, testable and readable.
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