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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

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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