core_lesson8

Lesson 8 - Making Objects the Main Star

Ch2 Sets

• A set is a sequential data structure
  • Order is not important
  • Doesn't have duplicates
• Denoted with {}
• Convert list to set by set([...])
• Not subscriptable
• Fast to check if element is in set
  • Use of hashing
• Set operations
  • Union a | b, a.union(b)
  • Intersection a & b, a.intersection(b)
  • Difference a \ b, a.difference(b)
  • Symmetric difference a ^ b, a.symmetric_difference(b)
  • Membership x in a, x not in a
  • Proper subset / superset a < b, a > b
  • Subset / superset a <= b, a >= b, a.issubset(b), a.issuperset(b)
• Frozen set
  • Immutable version of sets

Ch3 Classes

• Create a definition
  • Then instantiate a class instance
    • A.k.a object
• Has instance variables / attributes
• Convention
  • Use CamelCase for class names
• isinstance to check if an object is of a given class
• Constructors
  • __init__()
    • Will actually call __new__() first
    • Is a magic method

Ch4 Python Modules

• A module is just a .py file
  • A script that can be imported
• Put all the imports on top of he file
• __name__ special variable
  • Will have value __main__ when run as script
• Pathing
  • Python will first search current directory
  • Then search for sys.path

Ch5 Git Add Remote

• Connect local to remote repo git remote add origin URL
• Push to remote git push -u origin --all
• Remove origin git remote remove origin

Ch6-8 Object Methods

• Methods represent behaviour
• Magic methods / dunder (double underscore)
  • __str__ return a more readable string than the address
  • __add__ overload the + operator
    • Same with __sub__, __mul__, __truediv__, and__pow__
    • Also comparison operators
      • __lt__, __le__, __gt__, __ge__, __eq__, and __ne__
  • More dunders (out c)
    • __len__, __contains__, __getitem__, __setitem__, and __iter__

Ch9 File Handling

• Python handles 2 types of files
  • Binary
  • Text
• open(filename, option)
  • Option
    • r: read only mode
    • rb: read binary mode (read values in bytes)
    • w: write mode
      • a: append mode
      • r+: allows reading and writing at the same time
      • w+: clears the file and rewrites
  • Returns file object
    • .read(n) reads n characters
    • .readline() reads a line until \n
    • .write() writes line file
    • .close() good practice, prevents memory leaks
      • Use with statement instead of explicitly closing the file
    • .tell() return position of file pointer
    • .seek() move file pointer
• tempfile module, to create temporary files
• shutil module, provides high level operations
• os module, provides low level functions for file and directory manipulation
• os.path module, provides functions to deal with paths
• pathlib module,os.path but OOP

Ch10 Input Validation

• Defensive programming aka look before you leap
• Python recommends
  • Easier to Ask for Forgiveness than for Permission
    • Trust that they will do what they are supposed to do
    • Wraps statements with try ... except clauses
    • Maintains readability
    • Slightly more efficient
      • Not actively checking