Programming in Python : Dictionaries

Dictionaries are another data type in python. It can be think as a unordered collection of keys associated with values. The keys can be numbers, strings, or tuples. An empty dictionary is denoted by ‘{ }’. We can view all keys by simply calling keys(). The dict() constructor is using to build a dictionary.

>>> dic = {‘one’:1,’two’:2,’three’:3,’four’:4,’five’:5}

>>> dic
{‘four’: 4, ‘three’: 3, ‘five’: 5, ‘two’: 2, ‘one’: 1}

>>> dic[‘six’] = 6

>>> dic
{‘six’: 6, ‘three’: 3, ‘two’: 2, ‘four’: 4, ‘five’: 5, ‘one’: 1}

>>> del dic[‘five’]

>>> dic
{‘six’: 6, ‘three’: 3, ‘two’: 2, ‘four’: 4, ‘one’: 1}

>>> dic[‘seven’] = 7

>>> dic
{‘seven’: 7, ‘six’: 6, ‘three’: 3, ‘two’: 2, ‘four’: 4, ‘one’: 1}

>>> dic.key()

Traceback (most recent call last):
File “”, line 1, in
AttributeError: ‘dict’ object has no attribute ‘key’

>>> dic.keys()
[‘seven’, ‘six’, ‘three’, ‘two’, ‘four’, ‘one’]

>>> dic[‘seven’]
7
>>> dic[‘one’]
1

>>> ‘one’ in dic
True

>>> ‘three’ in dic
True

>>> ‘kjkk’ in dic
False

>>> del dic[‘one’]

>>> dic
{‘seven’: 7, ‘six’: 6, ‘three’: 3, ‘two’: 2, ‘four’: 4}

>>> dic.keys()
[‘seven’, ‘six’, ‘three’, ‘two’, ‘four’]

>>> dic.values()
[7, 6, 3, 2, 4]

>>> a=[(‘aass’,23),(‘iiii’,56),(‘dftj’,38)]

>>> a
[(‘aass’, 23), (‘iiii’, 56), (‘dftj’, 38)]

>>> dict(a)
{‘aass’: 23, ‘iiii’: 56, ‘dftj’: 38}

>>> b = dict(a)

>>> b
{‘aass’: 23, ‘iiii’: 56, ‘dftj’: 38}

>>> dict(jhjkhk = 433,jkhjkhk = 3434,iuijmkm = 344343)
{‘jkhjkhk’: 3434, ‘jhjkhk’: 433, ‘iuijmkm’: 344343}

>>> c = dict(jhjkhk = 433,jkhjkhk = 3434,iuijmkm = 344343)

>>> c
{‘jkhjkhk’: 3434, ‘jhjkhk’: 433, ‘iuijmkm’: 344343}

Advertisement

Programming in Python : Sets

Set is a data type in python. It is an unordered set of elements without duplicates. We can test an element is a member of the set. Set operations can operate on unique letters as given below.

>>> list1 = [‘apple’,’mango’,’pineapple’,’mango’,’apple’,’orange’]

>>> fruit = set(list1)

>>> fruit
set([‘orange’,’mango’,’apple’,’pineapple’])

>>> ‘mango’ in fruit
True

>>> ‘grape’ in fruit
False

>>> a = (‘abhilash’)

>>> a
‘abhilash’

>>> b = (‘abhijith’)

>>> b
‘abhijith’

>>> set(a)
set([‘a’, ‘b’, ‘i’, ‘h’, ‘l’, ‘s’])

>>> set(b)
set([‘a’, ‘b’, ‘i’, ‘h’, ‘j’, ‘t’])

>>> c = set(a)

>>> d = set(b)

>>> c
set([‘a’, ‘b’, ‘i’, ‘h’, ‘l’, ‘s’])

>>> d
set([‘a’, ‘b’, ‘i’, ‘h’, ‘j’, ‘t’])

>>> c-d
set([‘s’, ‘l’])

>>> d-c
set([‘j’, ‘t’])

>>> c |d
set([‘a’, ‘b’, ‘i’, ‘h’, ‘j’, ‘l’, ‘s’, ‘t’])

>>> c & d
set([‘a’, ‘i’, ‘b’, ‘h’])

>>> c ^ d
set([‘s’, ‘t’, ‘j’, ‘l’])

Programming in python: Tuples and sequences

Tuples consists of elements that are enclosed in parenthesis. The empty tuples is represented by ‘()’. The single element tuple is ending with a comma.

>>> t = (‘one’,’two’,’three’)

>>> t
(‘one’,’two’,’three’)

>>> e = ()

>>> e
()

>>> len(e)
0

>>> single = (‘one’,)

>>> single
(‘one’,)

>>> len(single)
1

The statement t = 1223,5676,’one’,’two’ is an example of tuple packing. The elements are packed together in a tuple. The sequence unpacking is also possible. ex: a,b,c,d = t

>>> t = 1223,5676,’one’,’two’

>>> t
(1223,5676,’one’,’two’)

>>> a,b,c,d = t

>>> a
1223

>>> d
‘two’

Programming in Python : Lists

The list data type in python allows more operations compared to the other data types. The items in the lists are enclosed by brackets ‘[]’. It may contain numbers, srtings, tuples or lists (nesting of lists).

>>> list1 = [1,2,3,’how’,’are’,’you’]

>>> list1
[1, 2, 3, ‘how’, ‘are’, ‘you’]

>>> list1[3]
‘how’

>>> list1[3:]
[‘how’, ‘are’, ‘you’]

>>> list1[:2]
[1, 2]

>>> list1[:2] = ‘and’

>>> list1
[‘a’, ‘n’, ‘d’, 3, ‘how’, ‘are’, ‘you’]

>>> list1[:2] = [‘and’]

>>> list1
[‘and’, 3, ‘how’, ‘are’, ‘you’]

>>> list1 = [12,34,56,’s’,’y’]

>>> list1
[12, 34, 56, ‘s’, ‘y’]

>>> list2 = [22,’22’]

We can add members of one list to the members of another list.
>>> list1[3:3] = list2

>>> list1
[12, 34, 56, 22, ’22’, ‘s’, ‘y’]

>>> list3 = [33,list2,’33’]

The following list is nested.
>>> list3
[33, [22, ’22’], ’33’]

>>> list3[1][1]
’22’

>>> list3[1][0]
22

The del statement :

It is used to remove an element from a list when the index of that element is given. It can be used to clear the entire list or remove the variable.

Programming in Python : Strings

Strings are also manupulated by python. Strings are represented within single quotes or double quotes. We can assign a string to a variable, and printed by using ‘print’. Strings can be surrounded by triple quotes “””. If there is \n the end of line, is echoed in the output.

>>> “Hello”+”world”
‘Helloworld’

>>> a=’how are you?’

>>> print a
how are you?

The slice notation :

The slice notation is used to return the elements of a list or characters of a string as specified by the indices.

>>> string1 = ‘hello world’

>>> string1
‘hello world’

>>> string1[0:1]
‘h’

>>> string1[0:4]
‘hell’

>>> string1[2:4]
‘ll’

>>> string1[:4]
‘hell’

>>> string1[3:]
‘lo world’

>>> string1[:0] = ‘Hai’
Traceback (most recent call last):
File “”, line 1, in
TypeError: ‘str’ object does not support item assignment

>>> string1[:0] + ‘Hai’
‘Hai’

>>> string1
‘hello world’

>>> string1[:] + ‘Hai’
‘hello worldHai’

>>> ‘Hai’ + string1[:]
‘Haihello world’

The negative indices are using to indicate from the right to the begining of the string.

>>> string1[-1]
‘d’

>>> string1[-4:-1]
‘orl’

>>> string1[-4:-2]
‘or’

>>> string1[-4:0]

>>> string1[-1:-4]

>>> string1[-11:-1]
‘hello worl’

Programming in Python : Arithmetic operations in python

Python is a functional programming language. Arithmetic operations are simply done as shown below in python interactive mode.

>>> 3+5
8

>>> (10+40)/10
5
A value can be assigned to sevaral variables simultaneously. Complex numbers are also supported. Imaginary numbers are written with a suffix j or J. In a complex number z, z.real and z.imag returns real and imaginary parts respectively. In interactive mode the last printed character is assigned to a variable’_’.

>>> x = y = z = 0

>>> -1j * 1j
(1+0j)

>>> a=678

>>> a*23
15594

>>> print _
15594

>>> _/22
708