Values and Types

Introduction to CMPUT 175 Python Review

• Overview of the review material focusing on basic values and types in Python.

Basic Data Types in Python

Integers (int)

• Definition: Integers are whole numbers that can be positive or negative without a decimal point.

• Storage: Integers can have as many digits as the memory allows.

• Basic Operations on ints:

  • Addition: 3 + 4

  • Subtraction: 9 - 5

  • Multiplication: -34 * 3

  • Division (floor division): 7 // 2

  • Exponentiation: 2 ** 128

  • Modulo operation: 32 % 3

    • Explanation of Modulo:

      • Returns the remainder after integer division.

      • Results always between 0 and one less than the divisor (right value):

        • Example: 1 % 3 = 1, 2 % 3 = 2, 3 % 3 = 0, etc.

      • Useful in data structures and algorithms for wrapping behavior.

Floating-Point Numbers (float)

• Definition: Floats are finite approximations of real numbers that include decimal points.

• Basic Operations on floats:

  • Addition: 5.0 + -2.4

  • Multiplication: 4.9 * 2

  • Subtraction: 0.2 - 0.5

  • Division: 7.0 / 2.0 (note automatic conversion of ints to floats when using / operator).

• Type Determination:

  • Use type() function to determine data types:

    • type(3) gives int

    • type(3.0) gives float

    • For division, type(7 // 2) is int but type(7.0 / 2) is float.

Text Representation

Strings (str)

• Definition: Strings are sequences of characters enclosed in quotes (single or double).

• Accessing Characters:

  • Indexing starts from zero, e.g., for string "Eddie", use:"Eddie"[0] to access the first letter.

• String Length: Use the len() function:

  • Example: len("Eddie") returns 5.

• Indexing: The last character is accessed with index one less than the length, e.g., "Eddie"[4].

String Operations

• Membership Testing: Check if a substring exists within a string using in operator.

  • Example: "Ed" in "Eddie" is True, while "ed" in "Eddie" is False.

• Case Sensitivity: Strings are case sensitive. Use .lower() to convert a string to lowercase and .upper() for uppercase.

• String Concatenation: Use the plus operator to join strings, e.g., "CMPUT" + "175".

Special Value: None

• Definition: None represents the absence of a value.

  • Recognizable by its capitalization.

  • Returns no output when evaluated in Python's interactive console.

• Future Relevance: None will be useful for representing nothingness in computations as discussed in future lessons.

Summary of Concepts

• Integer and floating-point representations in Python using int and float types.

• String manipulation using str type.

• Importance of None for value representation in applications.