Transcript PPTX SD - Problemspace

Chapter 5
Functions
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Overview
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Function Declaration
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Parameters
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Parameters
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Positional Arguments
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Keyword Arguments
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Default Arguments
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Return Values
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Return Values
If a return statement omits a return value, None is returned implicitly.
Likewise, if a function reaches the end of its evaluation without reaching a
return statement, the function also returns None.
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Docstrings
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Docstrings
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Docstring Conventions
• As a matter of consistency always use triple
quotes for docstrings even if it is a one line string,
• The docstring summary should begin with an
action verb (e.g., “Return this..”, “Do that..”)
• The docstring summary should end with a period.
• For multi-line documentation, the docstring
should begin with a one line summary, then one
blank line, and then the longer documentation.
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Scope
Python has three different kinds of scope:
1. the built-in scope, which is made up identifiers defined by Python,
2. the global scope, which is made up identifiers defined in a Python file but not
within a function, and
3. the function scope, which is made up identifiers (including parameters) defined in
a function.
Consider this simple example where these three different scopes are being used:
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Scope
A visualization of the three principle scopes in Python - built-in identifiers form the
outermost scope followed by global identifiers and function identifiers.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
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Scope
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Scope
In this example the function scope has a variable x which shadows the global scope.
The result is two different variables that happen to have the same name.
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Scope
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Code Repetition
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Code Repetition
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Code Repetition
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Code Repetition
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Top-Down Design
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Top-Down Design
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Top-Down Design
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Top-Down Design
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Top-Down Design
1. If we break the problem up into smaller parts,
we clarify the tasks that need to be done to
solve the problem.
2. Each smaller part is typically less complicated
than the whole, making the problem more
approachable.
3. Smaller parts may be reusable, reducing the
implementation size.
4. Breaking the problem up also allows us to
distribute the problem solving work, enabling
team work.
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Recursion
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Recursion
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Functions as Values
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Functions as Values
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