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Python Mini-Course University of Oklahoma Department of Psychology Day 1 – Lesson 4 Beginning Functions 4/5/09 Python Mini-Course: Day 1 - Lesson 4 1

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Lesson objectives 1. State the purpose of functions and modules in Python 2. Use built-in functions 3. Import modules and use imported functions 4. Create custom void functions 5. Discuss the concept of variable scope 4/5/09 Python Mini-Course: Day 1 - Lesson 4 2

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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) 4/5/09 Python Mini-Course: Day 1 - Lesson 4 3

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Functions We’ve already seen some functions: type() Type casting functions int(), float(), str() 4/5/09 Python Mini-Course: Day 1 - Lesson 4 4

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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/)http://docs.python.org/library/ You can also create and use add-in modules 4/5/09 Python Mini-Course: Day 1 - Lesson 4 5

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Using import To use a module, you first have to import it into your namespace To import the entire module import module_name To import specific functions from module_name import function_name 4/5/09 Python Mini-Course: Day 1 - Lesson 4 6

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The math module The standard math module includes: Number-theoretic and representation functions Power and logarithmic functions Trigonometric functions Hyperbolic functions Angular conversion Constants 4/5/09 Python Mini-Course: Day 1 - Lesson 4 7

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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) 4/5/09 Python Mini-Course: Day 1 - Lesson 4 8

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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 4/5/09 Python Mini-Course: Day 1 - Lesson 4 9

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More on Importing from math import * print sin(2) Be careful when using the import * command. It can easily lead to namespace conflicts. 4/5/09 Python Mini-Course: Day 1 - Lesson 4 10

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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." 4/5/09 Python Mini-Course: Day 1 - Lesson 4 11

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Composing functions def repeat_lyrics(): print_lyrics() repeat_lyrics() 4/5/09 Python Mini-Course: Day 1 - Lesson 4 12

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Functions with arguments def print_twice(in_text): print in_text print_twice(‘Spam’) print_twice(‘Spam’*4) 4/5/09 Python Mini-Course: Day 1 - Lesson 4 13

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Variable scope Scope The enclosing context where values and expressions are associated (partition in namespace) Variables inside functions are local 4/5/09 Python Mini-Course: Day 1 - Lesson 4 14

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Variable scope def cat_string(part1, part2): cat = part1 + part2 print cat cat_string(‘This ‘, ‘works’) print cat 4/5/09 Python Mini-Course: Day 1 - Lesson 4 15

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Documentation You can document functions in the code immediately after the function header Example: func_doc.py 4/5/09 Python Mini-Course: Day 1 - Lesson 4 16

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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)http://docs.python.org/library/math.html 4/5/09 Python Mini-Course: Day 1 - Lesson 4 17

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Python Functions : chapter 3

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