Day 1 lesson 4 beginning functions
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Day 1 – Lesson 4 Beginning Functions. Python Mini-Course University of Oklahoma Department of Psychology. Lesson objectives. State the purpose of functions and modules in Python Use built-in functions Import modules and use imported functions Create custom void functions

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Day 1 – Lesson 4 Beginning Functions

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Day 1 lesson 4 beginning functions

Day 1 – Lesson 4Beginning Functions

Python Mini-Course

University of Oklahoma

Department of Psychology

Python Mini-Course: Day 1 - Lesson 4


Lesson objectives

Lesson objectives

  • State the purpose of functions and modules in Python

  • Use built-in functions

  • Import modules and use imported functions

  • Create custom void functions

  • Discuss the concept of variable scope

Python Mini-Course: Day 1 - Lesson 4


Functions

Functions

  • Function

    • A named sequence of statements that performs a computation or action

  • Functions are called by name

    • Most functions accept inputs (arguments)

    • Some functions return results (return value)

Python Mini-Course: Day 1 - Lesson 4


Functions1

Functions

  • We’ve already seen some functions:

    • type()

    • Type casting functions

      • int(), float(), str()

Python Mini-Course: Day 1 - Lesson 4


Modules

Modules

  • Module

    • A file that contains a collection of related functions

  • Python has hundreds of standard modules

    • These are known as the Python Standard Library (http://docs.python.org/library/)

  • You can also create and use add-in modules

Python Mini-Course: Day 1 - Lesson 4


Using import

Using import

  • To use a module, you first have to import it into your namespace

  • To import the entire moduleimport module_name

  • To import specific functionsfrom module_name import function_name

Python Mini-Course: Day 1 - Lesson 4


The math module

The math module

  • The standard math module includes:

    • Number-theoretic and representation functions

    • Power and logarithmic functions

    • Trigonometric functions

    • Hyperbolic functions

    • Angular conversion

    • Constants

Python Mini-Course: Day 1 - Lesson 4


Using the math module

Using the math module

import math

degrees = 45

radians = degrees / 360.0 \

* 2 * math.pi

print math.sin(radians)

x = math.sin(degrees / 360.0 \

* 2 * math.pi)

Python Mini-Course: Day 1 - Lesson 4


Dot notation

Dot notation

  • Why did we use math.sin() instead of just sin()?

  • Try this: print sin(radians)

  • Dot notation allows the Python interpreter to organize and divide the namespace

Python Mini-Course: Day 1 - Lesson 4


More on importing

More on Importing

from math import *

print sin(2)

  • Be careful when using the import * command. It can easily lead to namespace conflicts.

Python Mini-Course: Day 1 - Lesson 4


Creating your own functions

Creating your own functions

  • You have to define the function

    • Example:

      def print_lyrics():

      print "I'm a lumberjack, and I'm okay."

      print "I sleep all night and I work all day."

Python Mini-Course: Day 1 - Lesson 4


Composing functions

Composing functions

def repeat_lyrics():

print_lyrics()

print_lyrics()

repeat_lyrics()

Python Mini-Course: Day 1 - Lesson 4


Functions with arguments

Functions with arguments

def print_twice(in_text):

print in_text

print in_text

print_twice(‘Spam’)

print_twice(‘Spam’*4)

Python Mini-Course: Day 1 - Lesson 4


Variable scope

Variable scope

  • Scope

    • The enclosing context where values and expressions are associated (partition in namespace)

  • Variables inside functions are local

Python Mini-Course: Day 1 - Lesson 4


Variable scope1

Variable scope

def cat_string(part1, part2):

cat = part1 + part2

print cat

cat_string(‘This ‘, ‘works’)

print cat

Python Mini-Course: Day 1 - Lesson 4


Documentation

Documentation

  • You can document functions in the code immediately after the function header

  • Example: func_doc.py

Python Mini-Course: Day 1 - Lesson 4


Before next time

Before next time

  • Practice creating and using your own functions (try the exercises on pp 26-28)

  • Practice using the math module (see http://docs.python.org/library/math.html for documentation)

Python Mini-Course: Day 1 - Lesson 4


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