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Questions and Answers
Repetition statements are also known as loops.
Repetition statements are also known as loops.
True (A)
Each repetition of an action in a loop is called a iteration.
Each repetition of an action in a loop is called a iteration.
True (A)
Definite iteration loops repeat an action until the program determines it needs to stop.
Definite iteration loops repeat an action until the program determines it needs to stop.
False (B)
The for loop in Python is a control statement that easily supports definite iteration.
The for loop in Python is a control statement that easily supports definite iteration.
In a for loop, eachPass must be a keyword.
In a for loop, eachPass must be a keyword.
The first line of code in a for loop is called the loop body.
The first line of code in a for loop is called the loop body.
The loop body of a for loop must be indented and aligned in the same column.
The loop body of a for loop must be indented and aligned in the same column.
If the exponent is 0, the loop body will execute once.
If the exponent is 0, the loop body will execute once.
A count-controlled loop iterates through a range of numbers.
A count-controlled loop iterates through a range of numbers.
The range function can't be used to specify an explicit lower bound.
The range function can't be used to specify an explicit lower bound.
Augmented assignment operators can only be used with arithmetic operations.
Augmented assignment operators can only be used with arithmetic operations.
An off-by-one error is a syntax error.
An off-by-one error is a syntax error.
The range function returns a tuple.
The range function returns a tuple.
Strings cannot be traversed with a for loop.
Strings cannot be traversed with a for loop.
The range function only accepts two arguments: start and stop.
The range function only accepts two arguments: start and stop.
Loops can only count upwards, never downwards.
Loops can only count upwards, never downwards.
Field width refers to the number of additional spaces in formatted output.
Field width refers to the number of additional spaces in formatted output.
The letter 's' is used to format integers.
The letter 's' is used to format integers.
The <precision> specifier is required when formatting floating-point numbers.
The <precision> specifier is required when formatting floating-point numbers.
Selection statements allow a program to make decisions based on a condition.
Selection statements allow a program to make decisions based on a condition.
Boolean values can only be represented as True or False in Python.
Boolean values can only be represented as True or False in Python.
4 != 4 evaluates to True.
4 != 4 evaluates to True.
An if-else statement is also known as a one-way selection statement.
An if-else statement is also known as a one-way selection statement.
When using if-else statements for error checking, the else block typically handles the error condition.
When using if-else statements for error checking, the else block typically handles the error condition.
elif cannot be used in multi-way selection statements.
elif cannot be used in multi-way selection statements.
Logical operators combine Boolean expressions.
Logical operators combine Boolean expressions.
The or logical operator returns True only if both operands are True.
The or logical operator returns True only if both operands are True.
The not operator inverts the value of a Boolean expression.
The not operator inverts the value of a Boolean expression.
In Python, the assignment operator has higher precedence than logical operators.
In Python, the assignment operator has higher precedence than logical operators.
Short-circuit evaluation means that the entire expression is always evaluated, regardless of intermediate results.
Short-circuit evaluation means that the entire expression is always evaluated, regardless of intermediate results.
The while loop is used for definite iteration.
The while loop is used for definite iteration.
A continuation condition is tested within the loop.
A continuation condition is tested within the loop.
An infinite loop occurs when the continuation condition always remains true.
An infinite loop occurs when the continuation condition always remains true.
The while loop is an entry-control loop.
The while loop is an entry-control loop.
The body of a while loop always executes at least once.
The body of a while loop always executes at least once.
A loop control variable's initial value affects how the loop operates.
A loop control variable's initial value affects how the loop operates.
A break statement exits the loop.
A break statement exits the loop.
The for and while loops are not interchangeable and cannot be converted into each other.
The for and while loops are not interchangeable and cannot be converted into each other.
random.randint() generates only integer numbers.
random.randint() generates only integer numbers.
The random module only supports generating integer numbers.
The random module only supports generating integer numbers.
Repetition statements are also known as segments.
Repetition statements are also known as segments.
The first line of code in a for loop is sometimes called the loop header.
The first line of code in a for loop is sometimes called the loop header.
In Python, s -= 5 is equivalent to s = s - 5.
In Python, s -= 5 is equivalent to s = s - 5.
The range function can only be used to generate sequences of numbers that count upwards.
The range function can only be used to generate sequences of numbers that count upwards.
In Python, 4 != 4 evaluates to True.
In Python, 4 != 4 evaluates to True.
Flashcards
Repetition statement
Repetition statement
Statement that repeats an action.
Iteration
Iteration
Each execution of a repetition statement.
Definite iteration
Definite iteration
Loop that repeats an action a predefined number of times.
For loop
For loop
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Loop header
Loop header
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Loop body
Loop body
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Augmented assignment
Augmented assignment
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Off-by-one error
Off-by-one error
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Range function
Range function
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Field width
Field width
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Format string and % operator
Format string and % operator
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Boolean data type
Boolean data type
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== (Equals)
== (Equals)
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!= (Not equals)
!= (Not equals)
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Selection statement
Selection statement
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If
If
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If-Else statement
If-Else statement
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Multi-way if statement
Multi-way if statement
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or
or
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and
and
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not
not
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Short-circuit evaluation
Short-circuit evaluation
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While loop
While loop
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Conditional iteration
Conditional iteration
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Continuation condition
Continuation condition
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Infinite loop
Infinite loop
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Entry-control loop
Entry-control loop
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Loop control variable
Loop control variable
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Break statement
Break statement
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Random module
Random module
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Random.randint
Random.randint
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Definite iteration
Definite iteration
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Body
Body
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Off-by-one error
Off-by-one error
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Selection statements
Selection statements
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Control statement
Control statement
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Entry-control loop
Entry-control loop
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Break
Break
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Indefinite iteration
Indefinite iteration
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Intialization
Intialization
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For loops
For loops
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Format string and %
Format string and %
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Boolean expressions
Boolean expressions
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If else
If else
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Random.randint
Random.randint
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Study Notes
Objectives
- Chapter 3 focuses on loops and selection statements in Python.
- The objectives cover writing different types of loops (fixed number, character traversal, counting up/down).
- Also covered are entry-controlled loops, selection statements, Boolean expressions, and exiting loops.
Definitive Iteration: The for Loop
- Repetition statements, also known as loops, allow for repeating an action.
- Each instance of an action being repeated is a pass or iteration.
- Loops can be definite (repeating a predefined number of times).
- Loops can be indefinite (performing an action until the program determines it needs to stop).
Executing Statements a Given Number of Times
- The
forloop is a control statement in Python that easily facilitates definite iteration. - Basic structure: `for
in range( ): ... - The first line of code in a
forloop is the loop header. - The rest of the code, known as the loop body, must be indented and aligned in the same column.
Example: Exponentiation Loop
- Computes the exponentiation for a non-negative exponent.
- If the exponent is 0, the loop body does not execute and the value of
productremains 1.
Count-Controlled Loops
- Loops can count through a range of numbers using the
rangefunction. - Explicit lower bound can be specified in the range.
Example: Bound-Delimited Summation
- Summing numbers within a specified range.
Augmented Assignment
- The assignment symbol can be combined with arithmetic and concatenation operators to provide augmented assignment operations.
a += 3is equivalent toa = a + 3.- Format:
<variable> <operator>= <expression>. - This is equivalent to:
<variable> = <variable> <operator> <expression>.
Loop Errors: Off-by-One Error
- Example of counting from 1 through 4.
- The loop actually counts from 1 through 3 if
range(1,4)is used. - This represents a logic error, not a syntax error.
Traversing Data Sequence Contents
rangereturns a list.- Strings consist of character sequences.
- Values in a sequence can be visited with a
forloop:for <variable> in <sequence>: <do something with variable>.
Specifying Steps in the Range
rangeexpects a third argument to specify a step value.theSumgives the sum, based on the specified condition.
Loops that Count Down
- Example given for a for loop that counts from 10 to 1.
Formatting Text Output
- Many data-processing applications output data in tabular format.
- Field width refers to the total number of data characters and additional spaces for a datum in a formatted string.
- It automatically starts in the first column
Formatting Text Output Examples using format % operator
- This version uses format strings and format operators but a single data value will be generated
dis used for integer formatting, instead ofs- Can also be used to show a sequence of calculations
Formatting Text Output using 'Float" Type
- Use %.f to format as a float and .
is optional
Selection: If and If-Else Statements
- Selection statements enable computers to make choices.
- The choices are based on a condition.
Boolean Type, Comparisons, Boolean Expressions
- Boolean data types include two values: true and false.
- Comparison Operators ( e.g. ==, !=, <, >, <=, >=) provide a "Meaning"
If-Else Statements (1 of 2)
- A two-way selection statement used to check inputs for errors.
If-Else Statements (Syntax)
- if
: - else:
One-Way Selection Statements
- Simplest form of selection is the
ifstatement: - if
<condition>:<sequence of statements>
Multi-Way If Statements
- Programs test conditions that entail more than two alternative courses of action.
- In programming, referred to often as a multi-way selection statement.
Multi-Way If Statements(2 of 3)
- Example of the program to convert number grades to letter grades
- if condition 1 is met do first
- elif condition 2 is met, do second
- else do the default statements if nothing else works
Logical Operators and Compound Boolean Expressions
- If either of two courses of action is true, below are two approaches to resolve
- Youcan use
elifto go through each statement but it can become complex - Or you can simplify and use
orin the comparison statement
Logical Operators and Compound Boolean Expressions (Truth Table)
- Some claims can be made from previous tables.
- Use A = True, B= False to show AND, NOT, OR statement
- Can be used with variable assignment
Logical Operators and Compound Boolean Expressions (Operator Precendence)
- Remember
nothas higher precedence thanand, oror
Short-Circuit Evaluation
- In (A and B), if A is false, the expression is false
- There is no need to run B
- In (A or B), if A is true, the expression is true
- Example is given to count a number, and show the evaluation if a condition is or is not completed
Conditional Iteration: The "While" Loop
whileloop describes the conditional iteration code- Example is given to take any string input until the use enters a sentinel value
""to quit and end the loop
The Structure and Behavior of a While Loop
- Called a continuation loop when it should continue with another condition
- Improper use may lead to an infinite loop
- Can test conditions at the top of the loop and only execute 0 or more times
The Structure and Behavior of a While Loop(Data)
- The first input statement initializes a variable to an initial value that the loop condition can test
Count Control with a While Loop
- Can create a count-controlled loop instead of a
forloop to iterate through something
The While True Loop and The Break Statement
- The while loop can and should be written correctly for readability
- Example is given with the true as the initial condition to prompt the statements
- It then tests a condition to
breakfrom the loop - Use if data == "": (no input)
The While Loop and the Break Statement (Grade conversion with Loop)
- Used to continuous take grades from user, until the user enters in an acceptable value
- You must
breakfrom the loop, or else it will continue indefinitely
The While True Loop and the Break Statement(Bool Loop)
- A boolean variable can be used to control the loop instead of a direct conditional
Random Numbers
- Programming has generating resources for generating random numbers
- the
randommodule provides functions for this
Random Numbers (simple guessing example function)
- used to create a simple random number game
random.randint* creates a random integer
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Description
Explore Python's loops and selection statements. Learn to write fixed number loops and use Boolean expressions. Understand definite iteration using 'for' loops and control statements.
