Function Calls Built-in Functions vsModules

Function Calls

Built-in Functions vs Modules

? Python supports expressions with math-like functions

? The number of built-in functions is small

¡ì A function in an expression is a function call

¡ì

? Function calls have the form

? Missing a lot of functions you would expect

name(x,y,¡­)

function

name

¡ì Example: cos(), sqrt()

? Module: file that contains Python code

argument

? Arguments are

¡ì A way for Python to provide optional functions

? Examples:

¡ì Expressions, not values

¡ì round(2.34)

¡ì To access a module, the import command

¡ì Separated by commas

¡ì max(a+3,24)

¡ì Access the functions using module as a prefix

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Example: Module math

>>> import math

>>> math.cos(0)

To access math

functions

Functions

require math

prefix!

1.0

>>> cos(0)

Traceback (most recent call last):

File "", line 1, in

NameError: name 'cos' is not defined

>>> math.pi

3.141592653589793

Module has

variables too!

>>> math.cos(math.pi)

Reading the Python Documentation

Other Modules

? os

Function

name

¡ì Information about your OS

¡ì Cross-platform features

Possible arguments

? random

¡ì Generate random numbers

¡ì Can pick any distribution

Module

? introcs

What the function evaluates to

¡ì Custom module for the course



¡ì Will be used a lot at start

-1.0

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Interactive Shell vs. Modules

Using a Module

Module Contents

""" A simple module.

This file shows how modules work

"""

Docstring (note the Triple Quotes)

Acts as a multiple-line comment

Useful for code documentation

Single line comment

? Launch in command line

? Type each line separately

? Python executes as you type

? Write in a code editor

(not executed)

# This is a comment

Commands

x = 1+2

Executed on import

x = 3*x

Not

a command.

x

¡ì We use Atom Editor

¡ì But anything will work

? Load module with import

import ignores this

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Using a Module

Module Contents

""" A simple module.

This file shows how modules work

"""

# This is a comment

¡°Module data¡± must be

x = 1+2 prefixed by module name

x = 3*x

Prints docstring and

x

module contents

Modules Must be in Working Directory!

Python Shell

>>> import module

>>> x

Traceback (most recent call last):

Module you want

is in this folder

File "", line 1, in

NameError: name 'x' is not defined

>>> module.x

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>>> help(module)

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Have to navigate to folder

BEFORE running Python

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Modules vs. Scripts

Module

Scripts and Print Statements

Script

? Provides functions, variables

¡ì Example: temp.py

? Behaves like an application

¡ì Example: helloApp.py

? import it into Python shell

>>> import temp

>>> temp.to_fahrenheit(100)

? Run it from command line:

python helloApp.y

212.0

>>>

Files look the same. Difference is how you use them.

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module.py

script.py

""" A simple module.

""" A simple script.

This file shows how modules work

"""

This file shows why we use print

"""

# This is a comment

x = 1+2

x = 3*x

Only difference

x

# This is a comment

x = 1+2

x = 3*x

print(x)

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User Input

>>> input('Type something')

Type somethingabc

No space after the prompt.

'abc'

>>> input('Type something: ')

Type something: abc

Proper space after prompt.

'abc'

>>> x = input('Type something: ')

Type something: abc

Assign result to variable.

>>> x

'abc'

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Numeric Input

¡ì int(), float(), bool(), etc.

>>> x = input('Number: ')

Number: 3

>>> x

Value is a string.

'3'

>>> x + 1

¡ì Error if cannot convert

TypeError: must be str, not int

? input returns a string

¡ì Even if looks like int

¡ì It cannot know better

? You must convert values

? One way to program

¡ì But it is a bad way

¡ì Cannot be automated

>>> x = int(x)

Must convert to

>>> x+1

int.

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