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 in Python.
• If x = 7 and y = 2, then x * y equals 14.
• A complex number in Python is denoted as 5 + 2j.

Python Converting

• The int() function converts a string to an integer.
• int("45") + float("5.5") results in 50.5.
• 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 "".join([a, b, c]) or f"{a}{b}{c}".
• "Python" + 3 would cause an error.

Basic Math

• 5 * (2 + 3) equals 25.
• If a = 8 and b = 4, a / b equals 2.0.
• (4 + 6) * 2 - 8 / 2 equals 16.
• Python raises a ZeroDivisionError when dividing by zero.
• int(4.9) results in 4.

Basic Modulus

• 10 % 3 returns 1.
• The modulus operator in Python is %.
• If x = 25, x % 2 equals 1.
• 15 % 5 results in 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] results in "nohtyP".
• len(" ") is 1.

String Methods

• The .upper() method 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] results in "fedcba".
• If s = "hello", s[:3] returns "hel".
• If s = "hello", s[-3:-1] is "ll".
• If s = "python", s[::2] is "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() or .isnumeric().
• "Python" in "I love Python" returns True.
• The .isalpha() method checks if a string contains only alphabetical characters.
• "hello world".find("world") returns 6.
• To verify if a string is entirely uppercase, use .isupper().
• "apple".islower() returns True.
• "abc123".isalnum() returns True.
• To check if a string is empty, use len(string) == 0 or string == "".