Untitled

• This notebook discusses Python control structures, including sequential, decision/selection, and repetition/iterative structures.
• Statements are executed based on conditions ("if"), repeatedly using loops ("for", "while"), or located in separate parts of a program (functions).

Control Structures

• Sequential: Instructions are executed in a normal, line-by-line flow
• e.g., A=5, B=6, Print(A+B)
• Decision/Selection: Control flow depends on a condition, moving in only one direction depending on the condition's parameter.
• Repetition/Iterative: Includes while and for structures, allowing code to be repeated.

Decisions with the "if" Statement

• Programs make decisions with IF statements.
• When a condition is met, one set executes, and another set runs if the condition is not fulfilled.
• if <expr>: an expression is evaluated in a Boolean context
• <statement> is a valid Python statement, and it must be indented.
• Python uses indentation for coding blocks, instead of curly brackets
• The delimiter is a colon (:) with indented spaces or tabs.

Conditional Logic and the if Statement

• The colon (:) is required after <expr>.
• To execute statements based on conditions an if statement used
• Code example:

x = 3
if x > 5:
    print("true")
    print(x)
else:
    print("false")
print ("Out of if block")

Sequence Control Structure

• A condition will result in a one-directional flow.
• The if/else double-selection structure flowchart example: if Grade >= 60 statement is true "passed" is printed, if not "failed" is printed.

Python Compound if Statement

• If the expression in the if statement is true, the statements within the if block are executed.
• If it's false, the statements are skipped.
• Execution continues with the statement immediately following the if block, or an else block.

Syntax of Python if Statement

• Syntax:

 if condition:
        statements

Tests and Relational Operators

• Python offers various relational operators, including:
  • == (equals)
  • < (less than)
  • > (greater than)
  • >= (greater than or equal to)
  • <= (less than or equal to)
  • != (not equal to)
  • is (is the same object as)
  • is not (is not the same object as)
  • in (is a member of)
  • not in (is not a member of)
• A single = and == have different usage.

Decision Making and if Statements

• Checks a condition.
• If true, executes a set of instructions.
• Python uses indentation for blocks.
• Example syntax:

if condition1:
    statement(s)
else:
    statement(s)

• The program checks if a number is positive or negative and displays an appropriate message.

Truthiness with if Statements

• Example conditions and results
• When x = 0, y = 5:
  • if x < y: #Truthy
  • if y < x: # Falsy
  • if x: # Falsy
  • if y: #Truthy
  • if x or y: #Truthy
  • >>> if x and y: # Falsy

The "if else" construct.

• Python allows you to define alternative paths if evaluation is not met.
• If <expr> is true, execute the first set of statements and skip the second, otherwise skip the first and execute the second.

if <expr>:
    <statement(s)>
else:
    <statement(s)>

Using if/else Structures

• In an example, the code prints "Passed" if Grade >= 60 or "False" if not.

The if, elif, else Selection Structure

• Syntax:

if <expr>:
    <statement(s)>
elif <expr>:
    <statement(s)>
...
else:
    <statement(s)>

• This structure is used when there are multiple conditions to check.

Iterative Statements and Loops

• Loop statements allow execution of one or more statements multiple times.
• Loop control statements alter the execution flow.
  • Break ends the loop
  • Continue skips to the next iteration
  • Pass functions as a placeholder
• The while Loop repeats a block as long as a condition is True.

while condition:
    statement(s)

• The "for" Loop executes over a sequence.

Repetition and the for Loop

• Function range is used to create a list of values.
• range(integer) values go from 0 up to given integer (i.e., not including)
• range(integer, integer) values go from first up to second integer
• range(integer, integer, integer) values go from first up to second integer but increases in intervals of the third integer.

  for counter in range (howmany):
and counter will have values 0, 1,.. howmany-1

Range Function and Loops

• Used when iteration needs to occur a specific number of times within a given range.
• Syntax: range(lower limit, upper limit, increment/decrement by)

Loop Control: Break & Continue

• "Break" terminates the "loop statement" and transfers the code to the next line.
• "Continue" skips the remainder of the body and initiates the next loop reiteration.

The pass Statement

• The pass statement does nothing, and is never executed.
• Used when a statement is syntactically required, however command execution or an implementation isn't required.
• Works as a placeholder
• Code example:

if fac is "senthil":
    print("Compiler SIR")
elif fac is "kiru":
    pass
elif fac is "GK":

Logical Operators

• and: Binary operator to true if both expressions are true
• or: evaluates to true if at least one expression is true
• not: Unary operator returns true if the expression is false.

Python Keywords

• Python has several reserved keywords
• and, continue, else, for, import, not, raise, assert, or

Augmented Assignment Symbols

• x = x + 5 is functionally equivalent to x += 5
• the same rule applies to any other mathematical symbol (*,**,/,%)