carmine / uni-py

Code from various online courses (coursera, udacity, etc.), in python

uni-py

Code from various online courses (coursera, udacity, etc.), in python

Prerequisites

Virtualenv

• Installing IPython on the mac is problematic.
• Probably better hygiene to use Virtualenv anyway.
• Instructions (assuming you have python and pip installed already):

pip install virtualenv
virtualenv class-env
source class-env/bin/activate
pip install IPython

Links

1. Idiomatic Python
2. Python 101

"Classes"

• Python 101
  • Summary:
    • Useful if you've read about Python before and are just trying to refresh your memory.
  • Nuggets:
    • In []: - this is the IPython prompt
    • In []: import this - the zen of python
    • flake8 package - the modular source code checker: pep8, pyflakes and co
    • Tuples are like lists, but are not mutable.
    • range/xrange - xrange gone in 3.x. range creates whole list, xrange is a generator.
      • So, if you create 1B numbers, range chews up memory.
    • dictionary
      • Dictionary views mutate as the underlying dictionary mutates.
      • use in, get takes default value, setdefault to set value if doesn't exist
    • Files - use with to open file, and have it closed when done
    • None is a singleton. Use cases are similar to using nil / null.
    • id(obj) return integer ID of the object
    • Modules - finding them through sys.path, PYTHONPATH env.
    • And iterator is something that satisfies the iterator protocol. Clue: If it's an iterator, you can use it in a for: statement.
    • A generator is a class or function that implements an iterator, i.e. that implements the iterator protocol.
    • Creating:
      • fred = ["a", "b"]
      • suzy = {"a": 1, 2: "b" }
      • help({})
    • For loops
      • Comprehension: brackets

        for x in [y for y in range(10) if y % 2 == 0]:
          print 'x: %s' % x
        

      • Generator: parentheses

        gen1 = (item.upper() for item in items)
        for x in gen1:
          print 'x:', x
        

    • Classes
      • class A(object): pass - derived from object (recommended)
        • a = A()
      • Instance Method:

        class B(object):
          def show(self):
            print 'hello from B'
        

      • Constructor:

        class B(object):
          def __init__(self, name):
            self.name = name
        
        class A(object):
          def __init__(self, items=None):
            if items is None:
              self.items = []
            else:
              self.items = items
        
        # inheritance
        class B(A):
           def __init__(self, name, size):
             super(B, self).__init__(name)
             # A.__init__(self, name)    # an older alternative form
             self.size = size
        
        

      • Class Method:

        class B(object):
        
            Count = 0
        
            def dup_string(x):
                s1 = '%s%s' % (x, x,)
                return s1
            dup_string = staticmethod(dup_string)
        
            @classmethod
            def show_count(cls, msg):
                print '%s  %d' % (msg, cls.Count, )
        
        def test():
            print B.dup_string('abcd')
            B.show_count('here is the count: ')