Python numbers, converting, concatenation and math

Python Numbers

• 10 + 2.5 equals 12.5
• 3.14 is an example of a float in Python
• 9 // 2 equals 4 (integer division)
• If x = 7 and y = 2, then x * y equals 14
• In Python, a complex number is denoted as 5 + 2j

Python Converting

• The int() function converts a string to an integer
• int("45") + float("5.5") equals 50
• If num = 10.25, str(num) returns "10.25"
• float("3") returns 3.0
• int("123abc") results in an Error

Python Concatenation

• "Hello" + " " + "World" outputs "Hello World"
• The + operator is used to concatenate two strings in Python
• "Python" + str(3) results in "Python3"
• To combine a = "Learn", b = "Python", and c = "3" into a single string, use f"{a}{b}{c}"
• "Python" + 3 will cause an error

Basic Math

• 5 * (2 + 3) equals 25
• If a = 8 and b = 4, then a / b equals 2.0
• (4 + 6) * 2 - 8 / 2 equals 16
• Python raises a ZeroDivisionError if you divide by zero
• int(4.9) equals 4

Basic Modulus

• 10 % 3 returns 1
• The modulus operator in Python is %
• If x = 25, x % 2 is 1
• 15 % 5 equals 0
• 7 % 4 returns 3

Strings

• The length of "Python" is 6
• Given s = "coding", s[2] returns 'd'
• The character at index -1 in the string "Hello" is 'o'
• "Python"[::-1] produces "nohtyP"
• len(" ") is 1

String Methods

• .upper() converts all characters in a string to uppercase
• "hello".capitalize() returns "Hello"
• .strip() removes leading and trailing whitespace from a string
• "Python".startswith("Py") returns True
• "Python".find("y") returns 1

Indexing and Slicing

• If s = "abcdef", s[1:4] returns "bcd"
• "abcdef"[::-1] produces "fedcba"
• If s = "hello", s[:3] returns "hel"
• If s = "hello", s[-3:-1] returns "ll"
• If s = "python", s[::2] produces "pto"

Checking Strings

• To check if "apple" is in "pineapple pie", use "apple" in "pineapple pie"
• "hello".endswith("lo") returns True
• To check if a string contains only digits, use .isdigit()
• "Python" in "I love Python" returns True
• .isalpha() checks if a string contains only alphabetical characters
• "hello world".find("world") returns 6
• .isupper() verifies if a string is entirely uppercase
• "apple".islower() returns True
• "abc123".isalnum() returns True
• To check if a string is empty, either len(string) == 0 or string == ""