Crash Course on Python - M - 02 - README.md

Python Key Concepts for Automation Part-02

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Expressions & Variables

• Expression: A combination of values and operators that produces a result.
  Example: 2 + 3

• Variable: A named container that stores a value.
  Example: x = 10

• Data Types:

  • int – Integer
  • float – Decimal number
  • str – String
  • bool – Boolean (True/False)

• Keywords are reserved words in programming languages that have special meanings and specific purposes.
  They cannot be used as variable or function names.

  Common Keywords and Their Uses:

  • in – Checks if a value exists in a sequence.
  • not – Negates a condition (logical NOT).
  • or – Returns True if at least one condition is True.
  • for – Used to create a loop over a sequence.
  • while – Starts a loop that runs while a condition is true.
  • return – Exits a function and returns a value.

These keywords help control the flow and logic of a program.

• Variable names are identifiers used to store data in programming. Choosing effective variable names is essential for writing readable, understandable, and maintainable code.
  • Use letters, digits, and underscores, but start with a letter – not a digit or special character.
  • Avoid special characters (like &, %, -).
  • Use camelCase or snake_case consistently.
  • Make names descriptive and meaningful.

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Type Conversion

• Implicit Conversion:
  Python automatically converts types.
  Example: 7 + 2.0 = 9.0

• Explicit Conversion:
  Use functions to convert types manually:

  str(25)   # '25'
  int(3.7)  # 3
  float(5)  # 5.0

Type Annotation

name: str = "Alice"
age: int = 25
score_list: list[int] = [90, 85, 78]

Arithmetic Operators

Operator	Meaning	Example	Result
+	Addition	2 + 3	5
-	Subtraction	5 - 2	3
*	Multiplication	2 * 3	6
**	Exponentiation	2 ** 3	8
**	Exponentiation	number ** 0.5	sqrt
**	Exponentiation	number ** (1/3)	cube_root
/	Division	5 / 2	2.5
//	Floor Division	5 // 2	2
//	Floor Division	-5 // 2	-3
//	Floor Division	5 // -2	-3
%	Modulo (Remainder)	5 % 2	1
>	Greater than	5 > 2	True
<	Less than	5 < 2	False
==	Equal to	5 == 5	True

Common Errors

• TypeError: Adding incompatible types Fix: Use str() to convert number to string before concatenation.

• ZeroDivisionError: Division by zero Fix: Validate the denominator before dividing.

Built-in Functions

Function	Purpose
print()	Displays output to the console
type()	Shows the data type of an object
str()	Converts values to string
sorted()	Sorts iterables and returns a new list
max()	Finds the highest value in a set or list
min()	Finds the lowest value in a set or list

print()

Purpose: Displays one or more values to the console.

Example:

name = "Python"
print("Welcome to", name)

Output: Welcome to Python

type()

Purpose: Returns the data type of a given object.

Example:

value = 42
print(type(value))

Output: <class 'int'>

str()

Purpose: Converts a value to a string data type.
Example:

age = 30
print("I am " + str(age) + " years old.")

Output: I am 30 years old.

sorted()

Purpose: Sorts elements in an iterable and returns a new list.
Example:

numbers = [5, 2, 9, 1]
print(sorted(numbers))

Output: [1, 2, 5, 9]

max()

Purpose: Returns the largest value from a list or multiple arguments.
Example:

scores = [85, 92, 78]
print(max(scores))

Output: 92

min()

Purpose: Returns the smallest value from a list or multiple arguments.
Example:

temperatures = [13, 18, 9, 21]
print(min(temperatures))

Output: 9

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Returning Values in Python

What are Return Values?

Return values allow a function to send a result back to the part of the code that called it.
Instead of just printing output, functions can return data for reuse or further processing.

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Using return in a Function

def area_triangle(base, height):
    return base * height / 2

area_a = area_triangle(5, 4)
area_b = area_triangle(7, 3)
sum = area_a + area_b
print("The sum of both areas is: " + str(sum))

Output:

The sum of both areas is: 20.5

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Returning Multiple Values

def convert_seconds(seconds):
    hours = seconds // 3600
    minutes = (seconds - hours * 3600) // 60
    remaining_seconds = seconds - hours * 3600 - minutes * 60
    return hours, minutes, remaining_seconds

hours, minutes, seconds = convert_seconds(5000)
print(hours, minutes, seconds)

Output:

1 23 20

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Functions That Return Nothing

def greeting(name):
    print("Welcome, " + name)

result = greeting("Christine")
print(result)

Output:

Welcome, Christine
None

None is a special data type that represents “no value.”

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Key Style Principles in Python

• Self-documenting code: Use meaningful variable and function names to make the code explain itself.
• Refactoring: Improve unclear code by renaming and reorganizing for clarity.
• Comments: Use # to add helpful notes or explain complex parts. Good comments clarify why, not just what.
• Consistency: Follow a style guide to keep code clean and predictable.
• Be a good neighbor: Write code that others can understand and build on.

Well-styled code = easier to read, fewer errors, and happier developers.

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Functions

• Key Terms

  • Return value: Result sent back from a function
  • Parameter: Input passed into a function
  • Refactoring: Improving code readability without changing functionality

• Skills Practiced

  • Writing functions with multiple parameters
  • Returning calculated results
  • Performing conversions and calculations
  • Combining text with return values in print() statements
  • Converting types with str()

• Example

def greet(name, age):
    return "Hello, " + name + "! You are " + str(age) + " years old."

print(greet("Amein", "8-80"))
Output:
Hello, Amein! You are 8-80 years old.

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Basic Comparisons and Logical Operators in Python

Basic comparisons:
> (greater than), == (equal to), != (not equal), < (less than)

Example:
print(10 > 1) -> True

Type mismatches cause errors:
Comparing different types like 1 < "1" raises a TypeError

Logical operators:
and, or, and not combine or reverse logical expressions

• The and operator returns True only if all conditions are True.

Example:
print(25 > 50 and 1 != 2) -> False

• or operator returns True if any one of the conditions is True.

Example:
print(25 > 50 or 1 != 2) -> True

• The not operator reverses the truth value of an expression.

Expression	Result
not True	False
not False	True

print(25 > 50 or 1 != 2) # True

print(not (25 > 50 or 1 != 2)) # False

Key Comparison Operators in Python

Numeric Comparison Operators

Operator	Name	Example	Meaning
==	Equality	a == b	True if a equals b
!=	Not equal to	a != b	True if a is not equal to b
>	Greater than	a > b	True if a is larger than b
<	Less than	a < b	True if a is smaller than b
>=	Greater than or equal to	a >= b	True if a is greater than or equal to b
<=	Less than or equal to	a <= b	True if a is less than or equal to b

Examples

print(32 == 30 + 2)        # → True
print(5 + 10 == 6 + 7)     # → False
print(4 / 2 < 8 - 4)       # → True
print(12 * 2 >= 24)        # → True

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String Comparison Operators

Operator	Description	Example
==	Equal to — returns True if strings are the same	"cat" == "cat" → True
!=	Not equal to — returns True if strings differ	"dog" != "cat" → True
>	Greater than — based on Unicode (alphabetical)	"zebra" > "apple" → True
<	Less than — checks if left comes before right	"apple" < "banana" → True
>=	Greater than or equal to	"abc" >= "abc" → True
<=	Less than or equal to	"abc" <= "bcd" → True

Examples & Concepts

• Comparing identical strings returns True:

print("a string" == "a string")  # True

• Different data types can't be compared using < or >:

print("Five" < 6)  # TypeError

• Unicode values are used in string comparisons:
  • Uppercase A–Z: Unicode 65–90
  • Lowercase a–z: Unicode 97–122

print("Brown" < "brown")  # True (because 'B' < 'b' in Unicode)

or Operator in Python

The or logical operator returns True if at least one of the expressions is True. It is used to combine conditions where only one condition needs to be satisfied.

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Truth Table

Expression 1	Expression 2	Result
True	True	True
True	False	True
False	True	True
False	False	False

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Example

country = "United States"
city = "New York City"

print(country == "New York City" or city == "New York City")  # → True

if Statement in Python

The if statement allows program to branch and execute code only when a specific condition is met. It’s fundamental for controlling program flow.

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Example Code

def hint_username(username):
    if len(username) < 3:
        print("Invalid username. Must be at least 3 characters long")

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Functions

• Defined using the def keyword.
• Accept parameters and return values.
• Promote reusable, modular code.

Example:

def greet(name):
    return "Hello, " + name

print(greet("Alice"))

Output:

Hello, Alice

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Conditionals (if, elif, else)

• Control flow based on logical conditions.
• if checks a condition; elif checks additional conditions; else catches all other cases.
• Use comparison (==, !=, >, <) and logical operators (and, or, not).

Example:

temp = 45

if temp > 65:
    clothing = "T-Shirt"
elif temp > 50:
    clothing = "Sweatshirt"
elif temp > 32:
    clothing = "Jacket"
else:
    clothing = "Heavy Coat"

print(clothing)

Output:

Jacket

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Writing if-elif-else blocks

temp = 60

if temp > 65:
    clothing = "T-Shirt"
elif temp > 50:
    clothing = "Sweatshirt"
elif temp > 32:
    clothing = "Jacket"
else:
    clothing = "Heavy Coat"

print(clothing)

Output:

Sweatshirt

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Logical and Comparison Operators

• Used to compare values or combine conditions.
• Case-sensitive with strings.

Example (string comparison):

print("blue" == "Blue")

Output:

False

Example (logical operation):

print((5 > 2) and (3 < 7))

Output:

True

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Returning results in functions

def safe_division(numerator, denominator):
    if denominator == 0:
        return 0
    return numerator / denominator

print(safe_division(10, 2))
print(safe_division(5, 0))

Output:

5.0
0

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Using nested and complex conditions

number = 25

if number <= 5:
    print("Small")
elif number == 33:
    print("Match")
elif number < 32 and number > 6:
    print("Between 6 and 32")

Output:

Between 6 and 32