2.1. Introduction to Python

2.1.1. Python Features

• Interpreted – platform independent, very high level, rapid development cycle

• Very clear syntax – easy to learn, even just by example

• Fully Object Oriented, but not mandated

• No need to initialize variables

  Python determines data type of variables by how they are used.

  • A number expressed as and integer is an int (i = 5).
  • A number with a decimal point is a float (x = 3.5).
  • Character data is put in quotes and is a str (string) (st = ‘Hello, World’).

• Advanced built-in data structures allows for rapid development.

2.1.2. Indentation and block-structure

• Use colon and indention to identify a code block.

• No need for semicolons or brackets:

  n = 9
  r = 1
  while n > 0:
      r = r * n
      n = n – 1
  print r

2.1.3. Strings

• Initialize strings with pairs of single quotes, double quotes, or triple quotes:

  a = '\t this starts with a "tab".'
  b = "this string has 'line feed'.\n"
  c = "backslash \"quotes\"."
  d = 'same for \'single\' quotes.'
  
  e = """The triple quote is nice for strings that take multiple
  lines. 'single' and "double" quotes do not need backslashes."""
  

• Merging variables with strings:

  st = "There are %d lines and %d characters in the file" % (chars, lines)
  

2.1.4. Introducing Lists

• Very flexible built-in data container
• Like an array, a list contains a sequence of data items
• A list can contain a mixture of data types including any number type, strings, tuples, lists, dictionaries, functions, objects of any type
• Mixture of data types allows easy creation of data structures

See also

Built-in List Operations and Examples of List Use

2.1.5. Introducing Tuples

• A tuple is a list that is immutable (can not be changed once created)

  x = (1, 2, 3)

• Use tuples when possible because they are more efficient than lists

• Operators and built-in functions (in, +, *, len(), min(), max()) may be used with tuples

• Tuples are used to facilitate saving multiple values returned from a function

>>> def swap(a, b):
...     return(b, a)
...
>>> x = 1
>>> y = 2
>>> x, y = swap(x, y)
>>> x
2
>>> y
1

See also

Tuples

2.1.6. Introducing Dictionaries

• A list of two item pairs (key, value)
• The key is immutable
• The value may be any object
• Provides an associative array functionality implemented using hash tables
• Built-in operators: len(), del()
• Dictionary methods: dict.clear(), dict.copy(), dict.get(), dict.has_key(), dict.items(), dict.keys(), dict.update(), dict.values()

See also

Dictionaries, Built-in Dictionary Operations