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Questions and Answers
What is the name of the approach used to break a large program into functions?
What is the name of the approach used to break a large program into functions?
Divide and conquer approach
Which of the following are benefits of using functions?
Which of the following are benefits of using functions?
A void function returns a value after executing its statements.
A void function returns a value after executing its statements.
False
What is the purpose of the pass keyword in Python?
What is the purpose of the pass keyword in Python?
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What is the difference between an argument and a parameter in Python?
What is the difference between an argument and a parameter in Python?
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A local variable declared inside a function can be accessed by statements in other functions.
A local variable declared inside a function can be accessed by statements in other functions.
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Global variables declared outside all functions can be accessed from any statement within the program file.
Global variables declared outside all functions can be accessed from any statement within the program file.
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What is the general format for declaring a global variable in Python?
What is the general format for declaring a global variable in Python?
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A global constant is a global name that references a value, and it can be changed during program execution.
A global constant is a global name that references a value, and it can be changed during program execution.
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What is the purpose of the random module in Python?
What is the purpose of the random module in Python?
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The randint function returns a randomly selected integer from the sequence generated by the range function.
The randint function returns a randomly selected integer from the sequence generated by the range function.
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What is the output of the expression random.randint(1, 10)?
What is the output of the expression random.randint(1, 10)?
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What is the purpose of the seed value in the context of random numbers?
What is the purpose of the seed value in the context of random numbers?
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The randrange function returns a randomly selected integer from the sequence generated by the range function, but excludes the end value.
The randrange function returns a randomly selected integer from the sequence generated by the range function, but excludes the end value.
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What is the range of values returned by the random function?
What is the range of values returned by the random function?
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What is the output of the expression random.uniform(1.0, 10.0)?
What is the output of the expression random.uniform(1.0, 10.0)?
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The math module offers functions essential for performing mathematical computations.
The math module offers functions essential for performing mathematical computations.
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What is the purpose of modularization in large, complex programming projects?
What is the purpose of modularization in large, complex programming projects?
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What is a menu-driven program?
What is a menu-driven program?
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The variable __name__ is automatically created when a Python source code file is loaded into the interpreter.
The variable __name__ is automatically created when a Python source code file is loaded into the interpreter.
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How do you ensure that the main function of a module only executes when the file is run directly and not when it is imported?
How do you ensure that the main function of a module only executes when the file is run directly and not when it is imported?
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You can use the turtle module for working with turtle graphical operations.
You can use the turtle module for working with turtle graphical operations.
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The square function takes ______ arguments to draw a square.
The square function takes ______ arguments to draw a square.
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The circle function requires arguments specifying the starting and ending locations of the circle.
The circle function requires arguments specifying the starting and ending locations of the circle.
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The line function draws a line between the two points defined by its arguments.
The line function draws a line between the two points defined by its arguments.
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What are the key advantages of modularizing turtle graphics code using functions?
What are the key advantages of modularizing turtle graphics code using functions?
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Functions stored in modules can only be called by the same program that it was defined in.
Functions stored in modules can only be called by the same program that it was defined in.
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Study Notes
Introduction to Functions
- Function: a group of statements within a program that performs a specific task
- Functions in a large program allow breaking down complex tasks into smaller, more manageable sub-tasks
- This is known as the divide and conquer approach
- A modularized program breaks down each task into its own function
Topics
- Introduction to Functions
- Defining and Calling a Void Function
- Designing a Program to Use Functions
- Local Variables
- Passing Arguments to Functions
- Global Variables and Global Constants
- Turtle Graphics: Modularizing Code with Functions
- Introduction to Value-Returning Functions: Generating Random Numbers
- Writing Your Own Value-Returning Functions
- The math Module
- Storing Functions in Modules
Benefits of Modularizing a Program with Functions
- Simpler code
- Code reuse (write the code once and call it multiple times)
- Better testing and debugging (can test and debug each function individually)
- Faster development
- Easier facilitation of teamwork (different team members can write different functions)
Void Functions and Value-Returning Functions
- Void function: simply executes the statements it contains and then terminates
- Value-returning function: executes statements, returns a value to the statement that called it
- Examples of value-returning functions include input, int, float
Defining and Calling a Void Function
- Functions are given names
- Function naming rules: cannot use keywords as a function name, cannot contain spaces, first character must be a letter or underscore, all other characters must be a letter, number, or underscore, uppercase and lowercase characters are distinct
- Function name should be descriptive of the task carried out by the function
- Function definition: specifies what the function does (e.g., def function_name():)
Defining and Calling a Void Function (Continued)
- Function header: first line of the function (e.g., def function_name(): )
- Block: set of statements that belong together in a function
- Calling the function: causes the interpreter to jump to the function and execute its statements; the interpreter then returns to the part of the program that called the function
- Function return: the interpreter jumps back to the program's location
Example of Defining and Calling a Function
- A function, called "message," is created in memory, containing the statements in the definition.
- Calling the function causes the program to execute these statements.
Defining and Calling a Void Function (Continued)
- Main function: the function called when the program starts; it calls other functions as needed to accomplish its tasks. It also contains the mainline logic of the program.
Indentation in Python
- Each block within a function must be indented the same number of spaces
- Use tabs or spaces to indent lines in a block, but not both in a single block
- IDLE and PyCharm indent lines in blocks automatically
- Blank lines within a block of code are ignored
Designing a Program to Use Functions
- Flowcharts show function calls, with vertical bars on either side of the rectangle that contains the function name
- Hierarchy charts (also called structure charts) show the relationships between functions in the form of boxes (where each function is a box), and lines that connect the boxes to illustrate how functions in the program call each other
Designing a Program to Use Functions (Continued)
- Flowcharts show the flow of logic; hierarchy charts show the relationship between functions
- IPO charts describe the input, processing, and output for each function
Local Variables
- Local variable: a variable being assigned a value within a function; it belongs only to that function
- Only code within the function can access the variable
- Trying to access the variable outside the function results in an error
Local Variables (Continued)
- Scope: the part of a program in which a variable can be accessed
- Local variables cannot be accessed prior to their definition
- Different functions can have local variables with the same name
Passing Arguments to Functions
- Argument: data passed into a function when it is called
- Parameter: variable that receives an argument passed into a function
- Arguments are placed in parentheses following the function's name
- Functions can use arguments in calculations
Passing Arguments to Functions (Continued)
- Parameter variable: variable that is assigned the value of an argument when the function is called
- Parameter and argument reference the same value
Passing Multiple Arguments
- Python allows writing a function to accept multiple arguments
- Parameter list replaces a single parameter
- Parameters in the list are separated by commas
- Arguments are passed by position to the corresponding parameters (first argument to first parameter, second to second, etc.)
Making Changes to Parameters
- Changes made to a parameter value within a function do not affect the argument
- This is known as pass-by-value
- Provides one-way communication between functions
Keyword Arguments
- Keyword argument: argument that specifies which parameter the value should be passed to
- Position of the argument in the function call is irrelevant when using keyword arguments
- Positional arguments must appear first in a function call that mixes positional and keyword arguments
Global Variables
- Global variable: a variable created by an assignment statement written outside of all functions
- The variable can be accessed from any statement in the program file (including inside functions)
- If a function needs to assign a value to a global variable, the global variable must be explicitly redeclared within the function
Global Variables (Continued)
- Reasons to avoid global variables: can make debugging difficult, functions that use global variables are usually dependent on those variables, makes functions harder to transfer to other programs, makes programs hard to understand
Global Constants
- Global constant: global name that references a value that cannot be changed
- Permissible to use global constants
- Simulate global constants in Python by creating a global variable and not re-declaring it within functions
Introduction to Value-Returning Functions: Generating Random Numbers
- Void function: a group of statements performing a specific task
- Call the void function when needed
- Value-returning function: similar to a void function, but it returns a value
- Value is returned to the part of the program that called the function
- If the function finishes executing with a return value, it's returned to the statement that called it
Standard Library Functions and the import Statement
- Standard library: pre-written functions that come with Python
- Library functions perform tasks programmers commonly need
- Viewed as a "black box"
- Some library functions built directly into Python interpreter
- To use, just call the function (e.g.
print())
Standard Library Functions and the import Statement (Continued)
- Modules: files storing standard library functions; they organize functions not built into the interpreter
- Modules are copied to the computer when Python is installed
Generating Random Numbers
- Random numbers are useful in many programming tasks
- The random module includes functions to work with random numbers
- Dot notation is used to call functions belonging to a module (e.g.
module_name.function_name())
Generating Random Numbers (Continued)
-
randintfunction: generates a random integer in a specified range - Returns the random integer
- Used anywhere in the program needing an integer
Generating Random Numbers (Continued)
-
randrange: similar to range, but returns a randomly selected integer from a sequence -
random: returns a random float between 0.0 and 1.0 -
uniform: returns a random float in a specified range
Random Number Seeds
- Random numbers are pseudo-random, generated by a formula
- Seed value initializes the formula
- Different series are generated by different seed values
- System time is used by default for a seed value
- Use
random.seed()to specify a seed.
Writing Your Own Value-Returning Functions
- To create a value-returning function, write a standard function but add return statements
- Return an expression (e.g, a sum of values or a result of another value-returning function)
- Values are returned to the part of the program that called the function
Example: How to Use the Return Value of a Function
- Example of function
sumthat accepts two arguments, and returns their sum; the main function callssumand stores the result in a variable
How to Use Value-Returning Functions
- Value-returning functions can be used in specific situations
- Example: prompt users for input
- Simplify complex mathematical expressions
Using IPO Charts
- IPO charts describe a function's input, processing, and output
- Tool for designing and documenting functions
- Lay outs functions in columns
- Briefly describes input, processing, and output
Returning Strings
- Functions can return strings (e.g., a user's name)
Returning Boolean Values
- Boolean functions return either
TrueorFalse - Used in decision and repetition structures
- Used to simplify input validation
Returning Multiple Values
- Functions can return multiple values using a comma-separated list after the
returnstatement - Calling a multi-returning function requires assigning each returned value to a separate variable
The math Module
- Part of the standard library
- Contains functions useful for performing mathematical calculations
- Typically accepts one or more values as arguments and returns the result
- Requires
import mathstatement at the top of the program
The math Module (Continued)
- Contains constants such as
math.piandmath.e - These are used in math calculations (e.g., for circle area) using dot notation
Storing Functions in Modules
- Organize code in large and complex programs
- Modularization: grouping related functions in modules
- Easier to understand, test, maintain, and reuse
- Import the module that contains the necessary functions
Menu Driven Programs
- Menu-driven programs display a list of operations to a user
- Users select an operation from a menu
- The program uses a decision structure to determine the chosen option and executes the corresponding operations.
- This usually repeats until the user decides to quit.
Conditionally Executing the main Function
- Modules can be run standalone or imported into other programs
- The program has a main() function (this is different from the main code block)
- The
if name mainblock is conditionally executed to control actions that only occur when the program runs as a standalone script, but not when it is imported into another program.
Turtle Graphics: Modularizing Code with Functions
- Functions can store commonly used turtle graphics operations
- Example: Draw a square with a specified location, width, and color.
- Parameter values define location, width, and color
- Example uses: Draw a square, draw a circle, draw a line
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