Python Data Types and Conversions

More Data Types

• int is used for positive or negative whole numbers.
  • Example: age = 24
• float is used for positive or negative numbers with one or more decimals.
  • Example: gpa = 4.0
• Even though 4.0 and 4 have the same value, 4 is an integer and 4.0 is a float.

Converting Data Types

• Changing a variable's data type is done through converting.

Converting to an Integer

• The int() function converts values to integers.
  • Example: cheese = int("3") converts the string "3" to the integer 3
• Converting a float to an integer drops the decimal and following numbers.
  • Example: peppers = int(2.8) results in peppers being assigned the integer value 2

Converting to a String

• The str() function converts values to strings.
  • Example: fries = str(30) converts the integer 30 to the string "30"

Converting to a Float

• The float() function converts values to floats.
  • Example: pizza = float(4) converts the integer 4 to the float 4.0

Converting Inputs

• Inputs are automatically accepted as a string.
  • To perform math operations on an input, it must be converted to an integer or float first.
  • Example:
    • family = int(input("How many family members do you have?"))

Concatenation

• Concatenation combines two strings together using the + sign.
• Example:
  • string1 = "Paragliding is"
  • string2 = "daring"
  • string3 = string1 + " " + string2
  • print(string3) outputs "Paragliding is daring"
• A substring is part of an existing string.

Concatenating an Integer

• Concatenation can only be done with strings and any integers must be converted to a string first.
  • Example: age = 12
  • print("You are " + str(age) + " years old.")

Modulus

• The modulus operator % returns the remainder of a division.
  • Example: fruits = 10 % 3 results in fruits being assigned the value 1 because 10 / 3 = 3 with a remainder of 1

Determining if a Number is Even or Odd

• The modulus operator is useful for determining if a number is even or odd.
  • Even numbers divided by 2 will have a remainder of 0, so even_number % 2 == 0 will be true.

Finding the Last 2 Numbers

• The modulus operator can find the last two digits of a number.
  • Example: number = 245
  • print(number % 100) outputs 45

Modulus in the Order of Operations

• The order of operations is:
  • Parentheses
  • Exponents
  • Multiplication/Modulus
  • Division
  • Addition
  • Subtraction
• Modulus has the same priority as multiplication and division, and execution proceeds from left to right.

Python Math

• Basic math operations:
  • Addition: c = a + b
  • Subtraction: c = a - b
  • Multiplication: c = a * b
  • Division: c = a / b
• Arithmetic can be performed within the print statement.
  • Example: print(number_butterflies + 15)

Division

• Dividing integers results in a float.
  • Example: bees = 16, flowers = 2, answer = bees / flowers results in answer being assigned the value 8.0

Order of Operations

• The designated order is as follows.
  • Parentheses
  • Exponents
  • Multiplication/Division
  • Addition/Subtraction
• Multiple operations of the same priority are performed from left to right.

Clarity and Readability

• Code should be clearly spaced, well-organized, and variables named appropriately for easy understanding.

Strings

• A string is a piece of information enclosed in quotation marks.
  • Can be declared using single or double quotes.
  • Example: pet = "dog" or pet = 'dog'
• Strings can contain multiple words, and even numbers.
  • Example: candy = "I have 10 chocolate candies and 13 strawberry candies."
• Strings are also referred to as string literals.
• A substring is a part of an existing string
  • Example: “chocolate” is a substring of the candy string.

Strings Can Hold Numbers

• A string can consist of only numbers.
  • Example: age = "15"
  • It is still considered a string, not an integer

Multiline strings

• Multiline strings can be created using three sets of quotes (single or double) before and after the text.
  • Example:
    • string1 = """I am part of a long string.
    • This the second line of code.
    • Look, I can keep going to the third line
    • and I am still being
    • assigned to the same variable."""

Indexing

• Indexing gets a character's location in a string, starting at zero.
• For the string "Coding is awesome!", the character "C" is at index 0.
  • string1 = "Coding is awesome!"
  • print(string1[5]) would print "g".
• Spaces count as an index value.
  • string1 = "Coding is awesome!"
  • print(string1[8]) prints "s".
• Negative indexing counts backwards, starting at -1 from the end.
  • string1 = "Coding is awesome!"
  • print(string1[-3]) prints "m".

Slicing

• Slicing extracts a portion of a string using indexes.
  • The syntax is string[start:end:skip].
  • start is the index to start at.
  • end is the index to end before.
  • skip is how many characters to skip (default is 1).
  • Example: string1 = "I love coding!"
  • print(string1[4:9]) prints "ve co"
  • print(string1[2:9:2]) prints "lv o"
  • Leaving a section blank goes to the beginning or end of the string.
  • print(string1[:5]) prints "I lov"

Reverse a String

• Slicing can also reverse a string.
  • string1 = "yodel"
  • reverse = string1[len(string1)::-1]
  • print(reverse)

Split a String

• The .split() method divides a string into substrings based on spaces.
  • Example: string1 = "I love spaghetti!"
  • print(string1.split())

Length of a String

• The len() function returns the number of characters in a string, including spaces, starting the count at 1.
  • Example: string1 = "I love spaghetti!"
  • print(len(string1)) outputs 17

Find a Character in a String

• The find() method returns the index of the first occurrence of a character in a string.
  • Example: string1 = "I love Mississippi!"
  • print(string1.find("s")) outputs 2
• The rfind() method returns the index of the first occurrence of a character in a string starting from the end.
  • Example: string1 = "I love Mississippi!"
  • print(string1.rfind("s"))

Checking Strings

• The keyword in checks if a string is present in a variable; returns a boolean.
  • Example: string1 = "I love Coding!"
  • check = "love" in string1
  • print(check) outputs True
• The keywords not in checks if a string is NOT present in a variable; returns a boolean.
  • Example: string1 = "I love Coding!"
  • check = "love" not in string1
  • print(check) outputs False
• String checks are case sensitive.