Python Mini-Course

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Day 1 Lesson 4Beginning Functions

• Python Mini-Course
• University of Oklahoma
• Department of Psychology

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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

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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)

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Functions

• Weve already seen some functions
• type()
• Type casting functions
• int(), float(), str()

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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/)
• You can also create and use add-in modules

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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

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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

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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)

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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

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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.

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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."

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Composing functions

• def repeat_lyrics()
• print_lyrics()
• print_lyrics()
• repeat_lyrics()

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Functions with arguments

• def print_twice(in_text)
• print in_text
• print in_text
• print_twice(Spam)
• print_twice(Spam4)

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Variable scope

• Scope
• The enclosing context where values and
  expressions are associated (partition in
  namespace)
• Variables inside functions are local

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Variable scope

• def cat_string(part1, part2)
• cat part1 part2
• print cat
• cat_string(This , works)
• print cat

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Documentation

• You can document functions in the code
  immediately after the function header
• Example func_doc.py

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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)