Indexing allows you to fetch a particular item in the sequence directly

Slicing operation which allows us to retrieve a slice of the sequence i.e. a part of the sequence

For example:

t = 12345, 54321, ‘hello!’

>>> t

(12345, 54321, ‘hello!’)

>>> t[0]

12345

>>> t[:-1]

(12345, 54321)

Each value has a corresponding key. Thus there exists a one-to-one relation between them

You cannot get a key by value, as otherwise

Keys are immutable but values can either be immutable or mutable

Dictionary cannot have a duplicate key thus a one-to-one relation must always exist between key and value. Assigning a value to an existing key will wipe out the old value

>>> d = {“Hello”:10, “world”:20}

>>> d

{‘world’: 20, ‘Hello’: 10}

>>> d[“Hello”]

10

>>> d[“Hello”] = 30

>>> d

{‘world’: 20, ‘Hello’: 30}

• Dictionaries support the following in-built methods, but are not limited to these:

d[k] retrieves a value from a dictionary

d[k]=x sets a value in the dictionary

d.has_key(k) tests for the presence of a keyword

d.get(k, d) returns a default if a key is not found

d.keys() returns a list of keys from a dictionary

d.values() returns a list of values

It is an immutable list. A Tuple can not be changed in any way once it is created.

>>> t = (“Hello”, 10, “world”, 20) >>> t (‘Hello’, 10, ‘world’, 20)

Like a list, all its elements are ordered. First element starts at index 0.

>>> t[0]

‘Hello’

Negative indices count from the end of the tuple, just like a list

>>> t[-1]

20

Slicing also works for tuple same as it works for list.

>>> t[1:3]

(10, ‘world’) # creates a new tuple

Unlike list, they have no in-built methods. So you cannot add, remove, index elements in a tuple.

Thus, they are truly immutable in a way that lets you write create write-protect data.

First element in the list starts at 0 index. >>> x[0] ‘Hello’

>>> type(x) # function type() specifies type of an object.

<type ‘list’> # x is of type list

>>> x[-1]

’20’

>>> x[-2]

‘World’

List can have items of different types unlike in C/C++ where we can have array of only single type.

Lists can be sliced, concatenated and so on: >>> x[:2] #list sliced to display first two elements

[‘Hello’, 10]

>>> x[:-1]

[‘Hello’, 10, ‘World’] # list sliced to drop 2 elements

>>> x[:1] + [‘Good Morning’] # Concatenate 2 lists

[‘Hello’, ‘Good Morning’]

Apart, from this you have several other in-built methods like append, count, extend, reverse, pop, etc to add, delete, count items, etc.

>>> x.append(40)

>>> x

[‘Hello’, 10, ‘World’, ’20’, 40]

• Unlike strings, which are immutable, it is possible to change individual elements of a list:

>>> a

[‘Hello’, 10, ‘World’, ’20’]

>>> x[1] = x[1] + 23

>>> print x [‘Hello’, 33, ‘World’, ’20]

List

Tuple

Dictionary

Sequence

>>> ’Hello World’ ’Hello World’ # using single quote

>>> “doesn’t” “doesn’t” # using double quotes

>>> ’”Yes,” he said.’ # A mix of both ’”Yes,” he said.’

>>> “\”Yes,\” he said.” ’”Yes,” he said.’

>>> u’Hello World’ # Creates a unicode string u’Hello World’

>>> “””Hello World””” # Using triple quote ‘Hello World’

>>> ”’Hello World”’ ‘Hello World’

The small ‘u’ in front of the quote indicates that a Unicode string is to be created

>>> r’Hello \n World’             # Creates a raw string that do

# not give special attention to

# escape sequences.

‘Hello \\n World’

Numbers

Strings

Numbers

Python supports four numeric types that all are immutable:

Integer

>>> a = 10 >>> b = 20 >>> a * b 200

Long Integer

Float

>>> a = 2.5 >>> b = 1.5 >>> a / b 1.6666666666666667

Complex

>>> x = 1 + 2j >>> x.real 1.0 >>> x.imag 2.0

Python is loosely typed in a way that names are not required to be declared for their types. You can simply assign any type of data to a single variable

For example:

>>> x = 1 # x is a name bound to value 1

>>> x = ‘Hello’ # same name now stores a string

>>> print x

Hello

Python is a strong object oriented in a way that everything is an object; be it is a string, number, function, exception, etc. everything is just an object.

On install, Python can be started easily by typing ‘python’ on the shell. On successful invocation of python a prompt >>> is displayed which can then be used to submit python commands/programs to python for running.

To exit this python shell, you can press Ctrl + z button and press Enter.

Active State’s python has a nice Python Editor that you can use to edit python programs. This editor also has a python shell where these programs are run. Moreover, this editor has a nice word auto-completion facility that can help you determine the possible attributes a module is exporting.

There are similar other python editors like UliPad (also provides a python shell), Crimson Editor, etc. Crimson editor is just a generic text editor much like TextPad and has no way to launch python shell for running programs.

The one IDE I like the most is Eclipse Ganymede. This is a generic SDK that can be complemented with PyDev Plug-in to enable Python and Jython editor. It comes with many goodies such as code completion, syntax highlighting, syntax analysis, refactor, debug and many others.

I use PythonWin or python shell alone for short test programs. For my run time environment, I prefer Eclipse

Python list of editors or IDEs is very long. Most of them are freeware / shareware.

www.python.org

www.activestate.com

Both the sites have vast documentation of library modules.