Building Blocks

Comments

Anything following a # is a comment.

>>> print 1      # this is a comment
1
>>> # This whole line is a comment

Numbers

Numbers can be integers or floating point. e.g.: 

    1
    -77777
    3.14159265
    1.5e+12

Complex numbers, hexadecimal & octal numbers, and 'long' integers are also supported.

Strings

Strings ("string literals", to be precise) are enclosed in quotes (single or double).
Multi-line strings can be enclosed in triple-quotes. 

    'x'
    "Hello, world"
    """Twas brillig and the slithy toves
    did gyre and gimble in the wabe."""

String literals that are next to each other are concatenated. e.g.: 

>>> print 'x' "y"
xy

Lists

Lists are like arrays in C, but they are dynamically allocated.
This means that they can grow to any size, without being fixed in advance.

List literals are written in square brackets; individual entries are separated by commas.

List indexing starts from 0. 

>>> x = ['a', 'b', 'c']
>>> print x[2]
c

Because Python is dynamically typed, list elements do not all have to be of the same type. 

>>> x = ['abc', 17.3]
>>> x = [1, ['abc', 17.3], 2]




Variables

Variables are similar to most other languages - a variable name is a series of alphanumeric characters; the first must be a letter. Names are case-sensitive.

Variables do not need to be declared. A variable is automatically allocated when a value is assigned to it. 

>>> x = 6
>>> print x * 9
54
>>> stringVariable27 = 'A string'
>>> print stringVariable27
A string
>>> y = x + stringVariable27
Traceback (most recent call last):
  File "", line 1, in ?
TypeError: unsupported operand types for +: 'int' and 'str'




Operators

Standard mathematical operators exist for numbers.
Some also apply to strings and lists.

Numbers Strings Lists
  +   Addition Concatenation Concatenation
  -   Subtraction / negation
  *   Multiplication Repetition Repetition
  /   Division
  %   Remainder Formatting


Logical operators are used for conditional expressions.
Similar to C, the logical value 'true' is represented by the numeric value 1, and 'false' by the numeric value 0.

or Logical or
and Logical and
not Logical negation
< <= > >= == != Numeric or string comparison
in String or list membership


Parentheses are used to group expressions. e.g.: 

>>> 1 + 2 * 3
7
>>> (1 + 2) * 3
9





Statements

Blocks of statements are defined by their level of indentation.
The first level of statements should have no indentation.
New levels are introduced by statements such as if, while, and for.

Assignment

>>> x = 7
>>> str = 'abc' * x



print

>>> print 'abc' * x
abcabcabcabcabcabcabc



pass

pass is a placeholder, that does nothing (a "no-op").




if / else

>>> if 1 > 2:
...     print "Something's wrong"
...
>>>
>>> if (x > 3) and (x < 4):
...     y = x
... else:
...     y = x * 2
...



while

>>> while x < 10:
...     x = x * 2
...



for

>>> for i in ['a', 'b']:
...     print i
...
a
b
>>> for j in range(0,3):
...     print j
...
0
1
2



Don't forget the colon at the end of if, while, and for statements.


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