Python Function
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| module | A module is simply a file containing Python code. Every file containing Python code and whose file name ends in .py is a Python module.
The code in a module is, of course, meant to be executed.
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| print() | built-in, This function prints, within the interactive shell, whatever argument is given to it.
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| input() | interact with the user
Python treats as a string whatever the user types
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| eval() | expect the user to enter a value that is not a string
need to explicitly ask Python to evaluate what the user types as a Python expression
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| eval( input() ) | expect the user to type an expression (a number, a list, etc.) when requested.
wrap the eval() function around the input() function
whatever the user types will be evaluated as an expression.
>>> x = eval(input(‘Enter x: ’))
Enter x: 5
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| One-Way Decisions | if temp > 86:
print(‘Its hot!’)
print(‘Be sure to drink liquids.’)
print(‘Goodbye.’)
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| Two-Way Decisions | 1 temp = eval(input(‘Enter the current temperature: ’))
2
3 if temp > 86:
4
5 print(‘It is hot!’)
8 else:
9
10 print(‘It is not hot.’)
13 print(‘Goodbye.’)
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| Iteration Structures |
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| sequences 2 types | A string can be viewed as a sequence of one-character strings;
a list is a sequence of objects of any type (strings, numbers, even other lists).
A task that is common to all sequences is to perform an action on every object in the sequence.
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| spelling iteration | 1 name = input(‘Enter a word: ’)
2 print(‘The word spelled out: ’)
3
4 for char in name:
5 print(char)
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| iterate over list | >>> animals = [‘fish’, ‘cat’, ‘dog’]
>>> for animal in animals:
print(animal)
fish
cat
dog
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| char | The variable char in
for char in name:
print(char)
is just variable names, chosen to make the program more meaningful.
Note: change the name of the for loop variable, we also need to change any occurrence of it in the body of the for loop.
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| range() | built in function
can iterate over the integers 0, 1, 2, 3, 4:
>>> for i in range(5):
print(i)
0
1
2
3
4
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| start, end, stop | >>> for i in range(1, 14, 3):
print(i)
The sequence printed by the for loop starts at 1, uses a step size of 3, and ends before 14. Therefore it will print 1, 4, 7, 10, and 13.
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| print() versus return | So f() prints the computed value, but it does not return it.
This means that f(2) returns nothing and thus evaluates to nothing in an expression.
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| Function Definitions Are “Assignment” Statements | 1 s = input(‘Enter square or cube: ’)
2 if s == ‘square’:
3 def f(x):
4 return x*x
5 else:
6 def f(x):
7 return x*x*x
The actual definition of f() depends on the input entered by the user at execution time.
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| Comments | for understanding of:
1. for the user
2. for developer
# comment
Avoid by
meaningful variable names, simple, well-designed code, makes program almost, self-explanatory.
Comments should identify the main components, explain tricky parts.
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| Docstrings | special comment added to the function definition, one that will be picked up by the help() tool.
This is a string that should describe what the function does and must be placed directly below the first line of a function definition.
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