Python Course Functions and Modules Slides

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8/30/22 Functions & Modules 2
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• Today
§ Lesson 3: Function Calls
§ Lesson 4: Modules
§ Videos 4.1-4.5
• Next Time
§ Video 4.6 of Lesson 4
§ Lesson 5: Function Defs
• Also skim Python API

Function Calls
• Python supports expressions with math-like functions
§ A function in an expression is a function call
• Function calls have the form
name(x,y,…)
• Arguments are
§ Expressions, not values
§ Separated by commas
function
name
argument

Built-In Functions
• Python has several math functions
§ round(2.34)
§ max(a+3,24)
• You have seen many functions already
§ Type casting functions: int(), float(), bool()
• Documentation of all of these are online
§ https://docs.python.org/3/library/functions.html
§ Most of these are two advanced for us right now
Arguments can be
any expression

Functions as Commands/Statements
• Most functions are expressions.
§ You can use them in assignment statements
§ Example: x = round(2.34)
• But some functions are commands.
§ They instruct Python to do something
§ Help function: help()
§ Quit function: quit()
• How know which one? Read documentation.
These take no
arguments

Built-in Functions vs Modules
• The number of built-in functions is small
§ http://docs.python.org/3/library/functions.html
• Missing a lot of functions you would expect
§ Example: cos(), sqrt()
• Module: file that contains Python code
§ A way for Python to provide optional functions
§ To access a module, the import command
§ Access the functions using module as a prefix

Example: Module math
>>> import math
>>> math.cos(0)
1.0
>>> cos(0)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'cos' is not defined
>>> math.pi
3.141592653589793
>>> math.cos(math.pi)
-1.0

>>> import math
>>> math.cos(0)
1.0
>>> cos(0)
>>> math.pi
3.141592653589793
-1.0
To access math
functions
Functions
require math
prefix!

>>> import math
>>> math.cos(0)
1.0
>>> cos(0)
>>> math.pi
3.141592653589793
-1.0
To access math
functions
Functions
require math
prefix!
Module has
variables too!

>>> import math
>>> math.cos(0)
1.0
>>> cos(0)
>>> math.pi
3.141592653589793
-1.0
• os
§ Information about your OS
§ Cross-platform features
• random
§ Generate random numbers
§ Can pick any distribution
• introcs
§ Custom module for the course
§ Will be used a lot at start
To access math
functions
Functions
require math
prefix!
Module has
variables too!
Other Modules

Using the from Keyword
>>> import math
>>> math.pi
3.141592653589793
>>> from math import pi
>>> pi
3.141592653589793
>>> from math import *
>>> cos(pi)
-1.0
• Be careful using from!
• Using import is safer
§ Modules might conflict
(functions w/ same name)
§ What if import both?
• Example: Turtles
§ Used in Assignment 4
§ 2 modules: turtle, introcs
§ Both have func. Turtle()
Must prefix with
module name
No prefix needed
for variable pi
No prefix needed
for anything in math

Reading the Python Documentation
http://docs.python.org/3/library

Reading the Python Documentation
Function
name
Possible arguments
What the function evaluates to
Module
http://docs.python.org/3/library

Interactive Shell vs. Modules
• Write in a code editor
§ We use VS Code
§ But anything will work
• Load module with import
• Launch in command line
• Type each line separately
• Python executes as you type

Using a Module
Module Contents
""" A simple module.
This file shows how modules work
"""
# This is a comment
x = 1+2
x = 3*x
x

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Single line comment
(not executed)

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Single line comment
(not executed)
Docstring (note the Triple Quotes)
Acts as a multiple-line comment
Useful for code documentation

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Single line comment
(not executed)
Commands
Executed on import

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Single line comment
(not executed)
Commands
Executed on import
Not a command.
import ignores this

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Python Shell
>>> import module
>>>
x

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Python Shell
>>> import module
>>>
NameError: name 'x' is not defined
x

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Python Shell
>>> import module
>>>
>>>
9
x
module.x
“Module data” must be
prefixed by module name

Using a Module
Module Contents
"""
# This is a comment
x = 1+2
x = 3*x
x
Python Shell
>>> import module
>>>
>>>
9
>>>
x
module.x
help(module)
“Module data” must be
prefixed by module name
Prints docstring and
module contents

Modules Must be in Working Directory!
Module you want
is in this folder

Modules Must be in Working Directory!
Module you want
is in this folder
Have to navigate to folder
BEFORE running Python

Modules vs. Scripts
Module
• Provides functions, variables
§ Example: temp.py
• import it into Python shell
>>> import temp
>>> temp.to_fahrenheit(100)
212.0
>>>
Script
• Behaves like an application
§ Example: helloApp.py
• Run it from command line:
python helloApp.py

Modules vs. Scripts
Module
• Provides functions, variables
§ Example: temp.py
• import it into Python shell
>>> import temp
>>> temp.to_fahrenheit(100)
212.0
>>>
Script
• Behaves like an application
§ Example: helloApp.py
• Run it from command line:
python helloApp.py
Files look the same. Difference is how you use them.

Scripts and Print Statements
module.py
"""
# This is a comment
x = 1+2
x = 3*x
x
script.py
""" A simple script.
This file shows why we use print
"""
# This is a comment
x = 1+2
x = 3*x
print(x)

module.py
"""
# This is a comment
x = 1+2
x = 3*x
x
script.py
""" A simple script.
This file shows why we use print
"""
# This is a comment
x = 1+2
x = 3*x
print(x)
Only difference

module.py script.py
• Looks like nothing happens
• Python did the following:
§ Executed the assignments
§ Skipped the last line
(‘x’ is not a statement)
• We see something this time!
§ Executed the last line
(Prints the contents of x)

module.py script.py
• Looks like nothing happens
§ Skipped the last line
(‘x’ is not a statement)
• We see something this time!
§ Executed the last line
(Prints the contents of x)
When you run a script,
only statements are executed

User Input
>>> input('Type something')
Type somethingabc
'abc'
>>> input('Type something: ')
Type something: abc
'abc'
>>> x = input('Type something: ')
Type something: abc
>>> x
'abc'
No space after the prompt.
Proper space after prompt.
Assign result to variable.

Making a Script Interactive
"""
A script showing off input.
This file shows how to make a script
interactive.
"""
x = input("Give me a something: ")
print("You said: "+x)
[wmw2] folder> python script.py
Give me something: Hello
You said: Hello
[wmw2] folder> python script.py
Give me something: Goodbye
You said: Goodbye
[wmw2] folder>
Not using the
interactive shell

Numeric Input
• input returns a string
§ Even if looks like int
§ It cannot know better
• You must convert values
§ int(), float(), bool(), etc.
§ Error if cannot convert
• One way to program
§ But it is a bad way
§ Cannot be automated
>>> x = input('Number: ')
Number: 3
>>> x
'3'
>>> x + 1
TypeError: must be str, not int
>>> x = int(x)
>>> x+1
4
Value is a string.
Must convert to
int.

Next Time: Defining Functions
Function Call
• Command to do the function
• Can put it anywhere
§ In the Python shell
§ Inside another module
Function Definition
• Belongs inside a module

Next Time: Defining Functions
Function Call
• Can put it anywhere
§ In the Python shell
§ Inside another module
Function Definition
• Belongs inside a module
Can call as many
times as you want
But only define
function ONCE
arguments
inside ()

Clickers (If Time)

Reading Documentation

Reading isclose
• Assume that we type
>>> import weird
>>> isclose(2.000005,2.0)
• What is the result (value)?
A: True
B: False
C: An error!
D: Nothing!
E: I do not know

Reading isclose
>>> import weird
>>> isclose(2.000005,2.0)
A: True
B: False
C: An error!
D: Nothing!
E: I do not know
CORRECT

Reading isclose
>>> import weird
>>> weird.isclose(2.000005,2.0)
A: True
B: False
C: An error!
D: Nothing!
E: I do not know

Reading isclose
>>> import weird
>>> weird.isclose(2.000005,2.0)
A: True
B: False
C: An error!
D: Nothing!
E: I do not know
CORRECT

Reading isclose
>>> import weird
>>> weird.isclose(2.0,3.0,4.0)
A: True
B: False
C: An error!
D: Nothing!
E: I do not know

Reading isclose
>>> import weird
>>> weird.isclose(2.0,3.0,4.0)
A: True
B: False
C: An error!
D: Nothing!
E: I do not know
CORRECT

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