Intro to Python

• 
• Python is an interpreted language.
• It
  • is object oriented, or not
  • is dynamically typed
  • has a huge support library
  • runs on many platforms.
  • is open source
  • is fairly popular
  • is named after Monty Python
  • has a c/c++ api, so you can extend it.
• Python
  • has dynamic garbage collection, no pointers or memory management.
  • has nice built in types.
  • looks very much like c/c++ on many instances.
• With python, and especially the libraries, it is possible to write hundreds of lines of assembly code in a single line of python.
• Caution: I am a c/c++ programmer
  • My code tends to look like it.
  • You will find python people who code differently.
• Versions
  • Python 2 is a legacy version of python.
    • It had a strong usage base.
    • It had many libraries, some of which have not been ported to python 3
  • Python 3 was released in 2008
    • Represents a major overhaul to the language.
    • Is not completely backwardly compatible with python 2
    • Most libraries have bee moved.
    • This is the modern version.
  • On mirkwood
    • python2 and python3 exist
    • python is a symbolic link to python2
    • This is because most of the linux install stuff was in python 2
    • I will let you know in a month what fedora 30 uses.
  • I am a python2 person, but I am going to try to do this with python33.
    • It is time to upgrade.
• What do I do with python.
  • I do a bunch of xml file processing to generate maps and statistics here
  • I frequency do conversion stuff like the database example I gave you.
  • I built a set of GUI interface control/data viz tools for my dissertation.
  • I am currently building a Database Interface for my Miniature collection.
    • Interact with file systems.
    • Interact with database
    • Display pictures
• Let's play a bit.
  • Interacting with the interpreter.
    • Just run python3
    • CTRL-D will exit.
    • This will do for now.
    • Later we will move to files.
• I use the Library Reference constantly.
  • I code in python with a book in my hands.
• Variables and basic types.
  • True, False and None are defined.
  • bool
    • True/False as above.
    • print(True and True)
    • x = 3 > 4
    • print(x)
    • and, or not
    • <, <=, >, >=, ==, !=
    • is and is not test to see if two things are the same object.
      • l = [1,2,3]
      • m = l this is a shallow copy.
      • n = l[:] this is a deep copy.
      • l is m
      • l is n
      • l is not n
  • type, id
    • Type identifies the type of an object.
    • ID returns the id of an object (an address I bet)
    • try type (l), type(x), id(l), id(m), id(n), id(x)
  • By the way, in the interpreter, you don't need print(xxx)
    • Just the variable name will print the object.
  • Numeric types: int, float, complex
    • type(3)
    • type(2.1)
    • type (3+2j)
    • int(4.999)
    • float(3)
    • +,-,*,/, //, %
    • abs, **
    • divmod(a,b) returns a pair (a//b, a%b)
    • casts as above.
  • strings
    • in single or double quotes, either.
    • '"Hello World"' is what you normally print.
    • Can be indexed a[4], with 0 based indexing
    • But can be indexed with negative numbers as well
    • Ranges can be extracted a[1:3]
      • Anything left empty means from the beginning
      • a[3:] or a[:4]
    • A third argument to this is a stride
      • a[::3]
    • There are MANY string methods
      • This is one of my reasons for reaching for python.
      • strip, split, upper, lower, are among my favorites
      • But I would look there before I did anything else.
    • + is stringcat.