21  Python Programming

21.1 Python Basics

• Entering expressions into the interactive shell
• The integer, floating-point, and string data types
• String concatenation and replication
• Storing values in variables
  • Assignment statements
  • Variable names
• Your first program
• Dissecting your program
  • Comments
  • The print() function
  • The input() function
  • Printing the user’s name
  • The len() function
  • The str(), int(), and float() functions

21.2 Manipulating Strings

• Working with Strings
  • String literals
    • Double quotes
    • Escape characters
    • Raw strings
    • Multiline strings with triple quotes
    • Multiline comments
  • Indexing and slicing strings
  • The in and not in operators with Strings
• Putting strings inside other strings
  • String interpolation
  • f-strings
• Useful String methods
  • upper(), lower(), isupper(), and islower() methods
  • The isX() methods: isalpha(), isalnum(), isdecimal(), isspace(), istitle()
  • The startswith() and endswith() methods
  • The join() and split() methods
  • Splitting strings with the partition() method
  • Justifying text with the rjust(), ljust(), and center() methods
  • Removing whitespace with the strip(), rstrip(), and lstrip() methods
  • Numeric values of characters with the ord() and chr() functions

21.3 Functions

• def statements with parameters
• Define, call, pass, argument, parameter
• Return values and return statements
• The None value
• Keyword arguments and the print() function
• The call stack
• Local and global scope
  • Local variables cannot be used in the global scope
  • Local scopes cannot use variables in other local scopes
  • Global variables can be read from a local scope
  • Local and global variables with the same name
• The global statement

21.4 Flow Control

• Boolean values
• Comparison operators
• Boolean operators
  • Binary boolean operators
  • The not operator
• Mixing Boolean and comparison operators
• Elements of flow control
  • Conditions
  • Blocks of code
• Program execution
• Flow control statements
  • if statements
  • else statements
  • elif statements
  • While loop statements
    • An annoying while loop
    • Input validation
  • Break statements
  • Continue statements
  • For loops and the range() function
    • An equivalent while loop
    • The starting, stopping, and stepping arguments to range()
• Importing modules
  • from and import statements
  • Useful modules from standard library:
    • pprint — Data pretty printer (helpful to print dictionaries)
    • Numeric and mathematical modules (math, random, fractions)
    • itertools — Functions creating iterators for efficient looping
    • functools — Higher-order functions and operations on callable objects
    • collections — Container datatypes (namedtuple, defaultdict, deque, OrderedDict)
• Ending a program early with the sys.exit() function

21.5 Data Structures

21.5.1 Lists and Tuples

• The list data type
  • Getting individual values in a list with indexes
  • Negative indexes
  • Getting a list from another list with slices
  • Getting a list’s length with the len() function
  • Changing values in a list with indexes
  • List concatenation and list replication
  • Removing values from lists with del statements
• Working with lists
  • Using for loops with lists
  • The in and not in operators
  • The multiple assignment trick
  • Using the enumerate() function with lists
  • Using the random.choice() and random.shuffle() functions with lists
• Augmented assignment operators
• Methods
  • Finding a value in a list with the index() method
  • Adding values to lists with theappend() and insert() methods
  • Removing values from lists with the remove() method
  • Sorting the values in a list with the sort() method
  • Reversing the values in a list with the reverse() method
• Sequence data types
  • Mutable and immutable data types
  • The tuple data type
  • Converting types with the list() and tuple() functions
• References
  • Identity and the id() function
  • Passing references
  • The copy module’s copy() and deepcopy() functions

21.5.2 Dictionaries and Structuring Data

• The dict data type
  • Dictionaries vs. lists
  • The keys(), values(), and items() methods
  • Checking whether a key or value exists in a dictionary
  • The get() method
  • The setdefault() method
• Pretty printing (pprint module)
• Using data structures to model real-world things

21.5.3 Sets, Named Tuples, Default Dictionaries, Counter, Deque

• The set data structure
  • Creating a set
  • Set operations
• The collections module
  • Named tuple
  • Default dictionary
  • Counter
  • The deque

21.6 File Handling

• Reading and Writing Files
  • Files and file paths
  • Backslash (\) on Windows and forward slash (/) on macOs and Linux
  • Using the / operator to join paths
  • The current working directory
  • The home directory
  • Absolute vs. relative paths
  • Creating new folders using the os.makedirs() function
  • Handling absolute and relative paths
  • Getting the parts of a file path
  • Finding file sizes and folder contents
  • Modifying a list of files using glob patterns (Interested? See pattern matching with Regex)
  • Checking path validity
• The file reading/writing process
  • Opening files with the open() function
  • Reading the contents of files
  • Writing to files
• Organizing Files
  • The shutil module
    • Copying files and folders
    • Moving and renaming files and folders
    • Permanently deleting files and folders
    • Walking a directory tree
• Error handling.

21.7 Debugging

• Raising exceptions
• Getting the traceback as a string
• Assertions
• Logging
  • Using the logging module
  • Don’t debug with the print() function
  • Logging levels
  • Disabling logging
  • Logging to a file
• Debugging in VSCode
  • Breakpoints
  • Debug Actions
    • Continue
    • Step in
    • Step over
    • Step out
    • Stop

21.8 Introduction to Object Oriented Programming (OOP)

• Classes and objects
• Accessing object variables
• Accessing object functions
• init() function