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README.md

Python 101

A beginners guide to getting started with python programming.

Installation instructions

We will be using Python 3.5 for the workshop.

Ubuntu

If you are using ubuntu, python will be installed by default. With Ubuntu 14.04, you will get python 3.4.

Lets install python 3.5.

Open a terminal by pressing CTRL + ALT + T.

Execute the following commands.

sudo add-apt-repository ppa:fkrull/deadsnakes
sudo apt-get update
sudo apt-get install python3.5

Type python3.5 and press enter, you should see something like this

$ python3.5
Python 3.5.0 (default, Sep 17 2015, 00:00:00)
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

Mac

  • To install any developer tools in OS X, XCode Command Line Tools are mandatory.

  • brew is extremely popular package manager in OS X. brew is similar to apt-get or yum in GNU/Linux operating system.

  • brew update && brew install python3. This will install latest Python version ie. Python 3.5.

  • Type python3.5 in terminal or shell.

~  python3.5
Python 3.5.0 (default, Sep 23 2015, 04:42:00)
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.72)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
  • If you don't like to use any package manager, download official python package.

Windows

If you are using windows, go to python downloads page and download python executable file.

Once it is downloaded, double click on it to install python.

Press Windows + R to open Run. Type python and press enter which opens up a python interpreter like this.

Alt windows

Open python idle and run

import os
import sys

print(os.path.dirname(sys.executable))

If cmd is not able to find python, then set PATH variable.

My computer -> Properties -> Advanced settingss -> Env variables -> New

PATH

Also include Scripts folder.

Content

Demo

Simple python projects that can be done in few minutes to few hours.

  • Tetris game
  • Weather widget
  • Django admin
  • Auto download subtitles for movies

Using the Python Interpreter

Calculator

Mathematical operator works similar to other languages.

>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5*6) / 4
5.0
>>> 8 / 5  # division always returns a floating point number
1.6

>>> 12 ** 2
144
>>> 2 ** 3
8
  • / always returns a float.
  • // can be used to discard the fractional part
  • % can be used to calculate the remainder
  • ** is used to calculate powers
  • = is used to assign a value to a variable

Quiz

What is simple and compound interest for 50,000 Rs at 8 % per annum for 10 years?

Variable assignment:

>>> a = 12
>>> b = 14
>>> a + b
26
>>> c = a + b
>>> c
26

In interactive mode the last printed expression is assigned to a variable named _

You don't need to define the type of variable before hand.

In [2]: a = 'hello'

In [3]: a
Out[3]: 'hello'

In [4]: a = 1

In [5]: a
Out[5]: 1

Quiz

Swap 2 variables with and without temporary variable

Strings

  • Strings can be enclosed in single quotes ('...')or double quotes("...").
  • \ Can be used for escaped characters
  • We can use a combination of single quotes and double quotes to avoid use of \ before escaped character
>>> 'This is BangPypers'
'This is BangPypers'
>>> "Hari don't know why"
"Hari don't know why"
  • print() function omits the enclosing quotes.
>>> print("Hari loves python")
Hari loves python
  • If you want to print the string as it is without interpreting prefaced \ as a special character then use raw strings
>>> print('home\abc')
homebc
>>> print(r'home\abc')
home\abc
  • If string is too long use triple quotes, ("""...""" or '''...''')
>>> print(""" Python is very easy
... I am learning python
... It is a beautiful language """)
Python is very easy
I am learning python
It is a beautiful language
>>>
  • Strings can be concatenated using + and repeated with *
>>> "p" + "y" * 5 + "thon"
'pyyyyython'
  • Two or more string literals, next to each other are automatically concatenated.
  • To concatenate a string literal and a string variable we must use +
>>> "hello" "world"
'helloworld'
>>> var = "abc"
>>> var + "def"
'abcdef'
>>> var "def"  # This will give syntax error
File "<stdin>", line 1
var "def"
^
SyntaxError: invalid syntax

String Indexing

  • First character of a string has index 0
  • Character is a string of size 1
  • If index is a negative number, it starts counting form the right
  • Negative indices start form -1
>>> word = "This is Python Bangpypers"
>>> word[0]  # Indexing starts from 0
'T'
>>> word[1]
'h'
>>> word[5]
'i'
>>> word[12]
'o'
>>> word[-1] # -ve indexing starts form -1 and it points to last character
's'
>>> word[-2]
'r'
>>> word[-5]
'y'
>>>

String Slicing

  • To obtain substring we use word slicing
  • In word[2:10], character at index 2 is included and at index 10 is excluded
  • Slices have default indices. An omitted first index defaults to 0 and omitted 2nd index defaults to size of the string
>>> word[15:-1]   # -ve index also works in slicing
'Bangpyper'
>>> word[15:]     # last index defaults to length of the string
'Bangpypers'
>>> word[1:]
'his is Python Bangpypers'
>>> word[:]       # First index defaults to 0
'This is Python Bangpypers'
>>> word[0:5]
'This '
  • Python strings are immutable
>>> word[5] = 'a'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

String Methods

  • capitalize(): Return a copy of the string with its first character capitalized and the rest lowercased
  • center(width[, fillchar]): Return centered in a string of length width
  • count(sub[, start[, end]]): Return the number of non-overlapping occurrences of substring sub in the range [start, end]
  • find(sub[, start[, end]]): Return the lowest index in the string where substring sub is found
  • format(): Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument.
>>> "The sum of 1 + 2 is {0}".format(1+2)
'The sum of 1 + 2 is 3'
  • isalnum(): Returns true if the string is alphanumeric
  • isalpha(), isdecimal(),isdigit(), or isnumeric()
  • join(): Return a string which is the concatenation of the strings, passed as argument in join.
#!/usr/bin/python

s = "-";
seq = ("a", "b", "c"); # This is sequence of strings.
print s.join( seq )
  • split: The method split() returns a list of all the words in the string, using str as the separator optionally limiting the number of splits to num.
#!/usr/bin/python

str = "Line1-abcdef \nLine2-abc \nLine4-abcd";
print str.split( )
print str.split(' ', 1 )

output:

['Line1-abcdef', 'Line2-abc', 'Line4-abcd']
['Line1-abcdef', '\nLine2-abc \nLine4-abcd']
  • There are many other predefined methods for strings, see here

String Formating printf-style

See the examples below

>>> print("My name is %s, I am %d yrs old" %("rajiv", 15))   # As tuples
My name is rajiv, I am 15 yrs old
>>> print('%(language)s has %(number)03d quote types.' %     # As dictionary
...       {'language': "Python", "number": 2})
Python has 002 quote types.

in and len()

  • len(str): This will return the length of the string, str
  • "abc" in str: Will return true if "abc" is substring of str

str is a string variable

Quiz

Check if given word is a polindrome?

Data Structures

Lists

  • Comma separated values between square brackets
  • Lists can also be indexed and sliced
  • List also support concatenation by +
  • Lists are mutable
  • To add items at the end of the list use append()
>>> list = [1, 2, 3, 4, 5, 6]
>>> list
[1, 2, 3, 4, 5, 6]
>>> list[0]                        # indexing returns the item
1
>>> list[4]                        # indexing returns the item
5
>>> list[-1]                        # indexing returns the item
6

>>> list[2:]                        # Slicing returns a new list
[3, 4, 5, 6]

>>> list + [12, 13, 14]             # list support concatenation
[1, 2, 3, 4, 5, 6, 12, 13, 14]

>>> list[4] = 1000                  # lists are mutable
>>> list
[1, 2, 3, 4, 1000, 6]

>>> list.append("Bangalore")        # Will append bangalore at the end of the list
>>> list
[1, 2, 3, 4, 1000, 6, 'Bangalore']

>>> list[2:4] = ["Python"]          # Slices can also be initialized
>>> list
[1, 2, 'Python', 1000, 6, 'Bangalore']

>>> len(list)                       # length of list can be found using len
6


>>> ### Nesting of list
...
>>>
>>> a = [1, 2, 3]
>>> b = ["m", "n", "o"]
>>> nlist = [a, b]
>>> nlist
[[1, 2, 3], ['m', 'n', 'o']]
>>> nlist[0]
[1, 2, 3]
>>> nlist[1]
['m', 'n', 'o']
>>> nlist[1][0]
'm'
>>> nlist[0][2]
3

List Methods
  • list.append(x): Add an item, x to the end of the list
  • list.extend(L): Append the list, L to list
  • list.insert(i, x): Insert item, x at index, i in the given list
  • list.remove(x): Remove item, x from the list
  • list.pop(i): remove an item at ith position from the list and return that value. If no index given it returns the last item.
  • list.clear(): removes all items form the list
  • list.index(x): index of item, x in the list
  • list.count(x): returns the number of times item, x appears in the list
  • list.reverse(): reverse the elements in the list in place
  • list.copy(): returns a copy of the list
  • list.sort(reverse=false): sort the list in ascending order if reverse is false and vice versa
The del statement
>>> a = [-1, 1, 66.25, 333, 333, 1234.5]
>>> del a[0]                  # delete an item at ith index
>>> a
[1, 66.25, 333, 333, 1234.5]
>>> del a[2:4]                # delete sublist
>>> a
[1, 66.25, 1234.5]
>>> del a[:]                  # delete whole list
>>> a
[]
>>> del a                     # delete the entire variable

Quiz:

numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Replace all even numbers with 0.

Tuples

  • All tuples are enclosed in paranthesis, to support nested tuples
  • But input may or may not be surrounded by parenthesis
  • Tuples are immutable
  • But they can contain mutable objects, i.e. lists
  • Empty tuples are created by empty pair of parenthesis
  • Singleton tuples are created by having tuple value followed by a comma.
  • t = 12345, 54321, 'hello!' is called tuple packing
  • the reverse is tuple unpacking i.e. x, y, z = t .
>>> t = 12345, 54321, 'hello!'
>>> t[0]
12345
>>> t
(12345, 54321, 'hello!')
>>> # Tuples may be nested:
... u = t, (1, 2, 3, 4, 5)
>>> u
((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
>>> # Tuples are immutable:
... t[0] = 88888
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> # but they can contain mutable objects:
... v = ([1, 2, 3], [3, 2, 1])
>>> v
([1, 2, 3], [3, 2, 1])
>>> empty = ()
>>> singleton = 'hello',
>>> len(empty)
0
>>> len(singleton)
1
>>> singleton
('hello',)

Sets

Please the examples below

>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
>>> print(basket)                      # show that duplicates have been removed
{'orange', 'banana', 'pear', 'apple'}
>>> 'orange' in basket                 # fast membership testing
True
>>> 'crabgrass' in basket
False

>>> # Demonstrate set operations on unique letters from two words
...
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a                                  # unique letters in a
{'a', 'r', 'b', 'c', 'd'}
>>> a - b                              # letters in a but not in b
{'r', 'd', 'b'}
>>> a | b                              # letters in either a or b
{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
>>> a & b                              # letters in both a and b
{'a', 'c'}
>>> a ^ b                              # letters in a or b but not both
{'r', 'd', 'b', 'm', 'z', 'l'}

Quiz

In [23]: A = { 0, 1, 2, 3, 4 }

In [24]: B = { 1, -2, 3, 4, 5, 6 }

In [25]: C = { 2, 4, 6, 7 }

Proove venn associative property with python A u (B n C) = (A u B) n (A u C)

>>> numbers = [1, 2, 3, 1, 4, 1, 2, 5]

Remove duplicate elements from a list?

Dictionaries

  • Called associative arrays in other languages
  • They are indexed by user defined keys
  • Keys are immutable
  • Keys can only be strings and numbers
  • Tuples can also be used as keys if they contain only strings and numbers
  • Any mutable object cannot be used as a key, e.g lists, slices etc
  • Dictionaries can be defined as unorderd set of "key, value" pairs
  • it is possible to delete a "key, value" pair using del key
  • list(d.keys()) returns the list of keys of dictionary d
  • sorted(d.keys()) to get the keys in sorted order
  • to check if key is present in dictionary we can use in keyword

Some examples

>>> score = {'harry': 75, 'snape': 97}
>>> score['ron'] = 50
>>> score
{'snape': 97, 'ron': 50, 'harry': 75}
>>> score['harry']
75
>>> del score['snape']
>>> score['voldemort'] = 60
>>> score
{'ron': 50, 'voldemort': 60, 'harry': 75}
>>> list(score.keys())
['voldemort', 'ron', 'harry']
>>> sorted(score.keys())
['ron', 'voldemort', 'harry']
>>> 'ron' in score
True
>>> 'harry' not in score
False
The dict() constructor
  • used to build dictionary form a sequence of "key, value" pairs
  • It can also be done by specifying pairs using keyword arguments
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
{'sape': 4139, 'jack': 4098, 'guido': 4127}
>>> dict(sape=4139, guido=4127, jack=4098)
{'sape': 4139, 'jack': 4098, 'guido': 4127}

Quiz

>>> data = {'bengaluru': '560029', 'moodbidri': '574227', 'mangaluru': '575001'}

Swap keys and values in a dictionary

Control Flow Tools

if Statement

See the example below

>>> # Program to find if number is multiple of 2 or 3
...
>>> x = int(input("Please enter an integer number: "))
Please enter an integer number: 56
>>> if x%2 == 0:
...     print("x is a multiple of 2")
... elif x%3 == 0:
...     print("x is a multiple of 3")
... else:
...     print("x is not a multiple of 2 or 3")
...
x is a multiple of 2
Note
  • There can be zero or more elif block and else block is optional

while loop

Lets see this with the help of an example

>>> # first n Fibbonaci numbers
>>> n = 20               # single assignment
>>> a, b = 0, 1          # multi assignment
>>> while n > 0:
...     print(a)
...     a, b, n = b, a+b, n-1         # multi assignment
...
0
1
1
2
3
5
8
13
21
#deleting the rest.
To Note here apart form syntax of while
  • we can assign variables in the same line as shown in above example
  • print is printing each output in different lines
Conditions in python
  • any non-zero integer value evaluates to true and zero is false
  • condition can also be a string or list value (anything with non-zero length is true)
  • Empty list, string or any sequence is false
  • standard comparison operators are: <, >, ==, <=, >=, and !=
More about print statement
  • you can print any number of values using print statement followed by end of line
>>> a, b = 10, 12
>>> print("value of a is: ", a, "value of b is: ", b)
value of a is:  10 value of b is:  12
  • To avoid end of line use the keyword argument end .
>>> a, b = 0, 1
>>> while b < 1000:
...     print(a, end=',')
...     a, b = b, a+b
...
0, 1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,

for Statements

See the example below to understand about for statement in python

>>> ## To capitalize each statement in a string
... stringList = ["ravi got  his pocket money.",
                  "he decided to buy an ice cream.",
                  "he ran to the ice ream shop, but in hurry he forgot the money",
                  "ravi came back home and kept the money in his piggy bank"]
>>> for str in stringList:
...     print(str.capitalize())
...
Ravi got  his pocket money.
He decided to buy an ice cream.
He ran to the ice cream shop, but in hurry he  forgot the money
Ravi came back home and kept the money in his piggy bank
  • If the sequence itself needs to be modified while looping then its recommended to create a copy of same sequence using slice.
>>> for w in words[:]:  # Loop over a slice copy of the entire list.
...     if len(w) > 6:
...         words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
Looping over integers
  • Use range() function
  • range() can be used in three ways
  • range(n): will contain numbers form 0 through n-1
  • range(x, y): will start from x and end at y - 1
  • range(x, y, z): will start at x and continue as x + z, x + 2z until x + kz is less than y
range(5, 10)
   5 through 9

range(0, 10, 3)
   0, 3, 6, 9

range(-10, -100, -30)
  -10, -40, -70

To iterate over indices of a sequence

>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)):
...     print(i, a[i])
...
0 Mary
1 had
2 a
3 little
4 lamb

To iterate over dictionary

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
...     print(k, v)
...
gallahad the pure
robin the brave
>>> for i, v in enumerate(['tic', 'tac', 'toe']):
...     print(i, v)
...
0 tic
1 tac
2 toe

>>> for i in reversed(range(1, 10, 2)):
...     print(i)
...
9
7
5
3
1
  • To convert range into a list use list(range(5))
input()
  • Input is taken as a raw string which is then typecasted into its respective type.

pythons break continue and else

  • break: breaks out of the loop
  • continue: continues with the next iteration of the loop
  • else: It is executed when loop terminates through exhaution of the list (in case of for) or when loops condition becomes false (in case of while)
>>> for n in range(2, 10):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
The pass statement
  • It does nothing
>>> if True:
...    pass
>>>

Functions

Defining functions

Keyword def is used to create new function.

>>> def sum_n(n):
...     """ Prints sum of n natural numbers. """
...     print(n * (n + 1) / 2)
...

def is followed by function name sum_n, followed by arguements in parens n.

Statements followed by definition form body of function and they should be indented properly.

It can also have doc string to summarize what a function does. This is optional.

You can check whether an object is a function.

>>> type(sum_n)
<class 'function'>

Calling a function with approriate arguements executes the function.

>>> sum_n()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: sum_n() missing 1 required positional argument: 'n'
>>> sum_n(5)
15.0

Functions are objects. They can be passed around just like variables.

>>> add_n = sum_n
>>> add_n(5)
15.0

Return statement

Every function returns some value.

If user doesn't return any value, None will be returned.

>>> x = sum_n(5)
15.0
>>> print(x)
None

Values can be returned from function using return statement.

We can modify previous function to return value instead of printing it.

>>> def sum_n(n):
...     """ Returns sum of n natural numbers. """
...     return (n * (n + 1) / 2)
...
>>> x = sum_n(5)
>>> print(x)
15.0

Function arguments

Arguements can be either positional or keyword.

>>> def power(base, exponent):
...   return pow(base, exponent)
...
>>> power(2,  3)
8
>>> power(base=2, exponent=3)
8

Keyword arguements can be passed in any order.

>>> power(exponent=3, base=2)
8
>>> power(base=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  TypeError: power() missing 1 required positional argument: 'exponent'

We can assign default values to arguements to make them optional.

>>> def power(base, exponent=1):
...     return  pow(base, exponent)
...
>>> power(2)
2
>>> power(2, 3)
8
>>> power(exponent=3, base=2)
8

Builtin functions

Python has some builtin functions which are always available.

>>> help()


>>> print('python')
python


>>> score = [45, 67,  89, -12]
>>> sum(score)
189
>>> len(score)
4
>>> max(score)
89
>>> min(score)
-12


>>> range(5)
range(0, 5)
>>> list(range(5))
[0, 1, 2, 3, 4]


>>> pow(3, 4)
81

Full list of functions can be found here

Lets try to understand Lambda.

Small anonymous functions can be created with the lambda keyword

def sumof(x,y):
    return x+y

Above function can also be represented using lambda

lambda x,y: x+y

Lambda functions can be used wherever function objects are required. Said that, let us try some inbuilt functions like map, filter

As help help of map

map(func, *iterables) --> map object
 |
 |  Make an iterator that computes the function using arguments from
 |  each of the iterables.  Stops when the shortest iterable is exhausted.

we either can define a function first and then pass it as first param, or use lambda instead.

map(sumof, [1,2,3], [4,5,6])

or

map(lambda x,y: x+y, [1,2,3], [4,5,6])

File handling

Files can read/write using open function.

You should pass filename(string) as argument.

You can also pass mode('r', 'w'), which is optional.

>>> f = open('data.txt')
>>> f
<open file 'data.txt', mode 'r' at 0x7fd3513d54b0>
>>> f = open('data.txt')
>>> for line in f:
...   print(line)
...
If you are reading this using python,

You are on your way to become awesome python programmer.

Now that you have read the file,

try writing some text into a file.

>>>

Lets create and write something into a file.

>>> f = open('story.txt')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'story.txt'
>>> f = open('story.txt', 'w')
>>> f.write('Once there lived a python programmer.')
>>> f.write('foo bar baz.')
>>> f.write('more foo')
>>> f.close()

Classes

A class is a specification (think of it as a blueprint or pattern and a set of instructions) of how to provide some service. Engineers and construction and factory workers use blueprints to build cars, buildings, bridges, virtually anything. Tailors, seamsters, printers use patterns to make the clothes we wear, books we read. Chefs follow recipes to put together meals.

>>> class Maths:
    def sumof(self, x, y):
        return x+y
    def mulof(self, x, y):
        return x*y

>>> obj = Maths()
>>> obj.sumof(3,4)
7
>>> obj.mulof(3,4)
12

Common mistakes while coding during initial days

>>> class Maths:
    def sumof(x, y):
        return x+y
    def mulof(x, y):
        return x*y

>>> obj = Maths()
>>> obj.sumof(3,4)
Traceback (most recent call last):
  File "<pyshell#49>", line 1, in <module>
    obj.sumof(3,4)
TypeError: sumof() takes 2 positional arguments but 3 were given

Below example from taken from http://anandology.com/python-practice-book/object_oriented_programming.html#classes-and-objects

class BankAccount:
    def __init__(self):
        self.balance = 0

    def withdraw(self, amount):
        self.balance -= amount
        return self.balance

    def deposit(self, amount):
        self.balance += amount
        return self.balance

>>> a = BankAccount()
>>> b = BankAccount()
>>> a.deposit(100)
100
>>> b.deposit(50)
50
>>> b.withdraw(10)
40
>>> a.withdraw(10)
90

class BankAccount:
    def __init__(self, initial_balance=0):
        self.balance = initial_balance

    def withdraw(self, amount):
        self.balance -= amount
        return self.balance

    def deposit(self, amount):
        self.balance += amount
        return self.balance
>>> obj = BankAccount(200)
>>> obj.balance
200
>>> obj.withdraw(50)
150
>>> obj.deposit(150)
300

Use docstring while writing code, that can be used to create documentation or while doing help to the object

>>> class BankAccount:
    """This class can be used to get the bank account details
       and also to do transaction.
    """
    def __init__(self, initial_balance=0):
        """Account holder can open their account with certail
           Initial balance, otherwise initial balace will be 0
        """
        self.balance = initial_balance

    def withdraw(self, amount):
        """This function can be used to withdraw amount from
           your account.
        """
        self.balance -= amount
        return self.balance

    def deposit(self, amount):
        """This function can be used to deposit amount into
           your account.
        """
        self.balance += amount
        return self.balance

>>> help(BankAccount)
Help on class BankAccount in module __main__:

class BankAccount(builtins.object)
 |  This class can be used to get the bank account details
 |  and also to do transaction.
 |
 |  Methods defined here:
 |
 |  __init__(self, initial_balance=0)
 |      Account holder can open their account with certail
 |      Initial balance, otherwise initial balace will be 0
 |
 |  deposit(self, amount)
 |      This function can be used to deposit amount into
 |      your account.
 |
 |  withdraw(self, amount)
 |      This function can be used to withdraw amount from
 |      your account.

Inheritance

A language feature would not be worthy of the name “class” without supporting inheritance. The syntax for a derived class definition looks like this:

class DerivedClassName(BaseClassName):
    <statement-1>
    .
    .
    .
    <statement-N>

Example

>> class Alto:
    def price(self):
        return '3L INR'
    def power(self):
        return '800cc'
    def maker(self):
        return 'Maruti'

>>> obj = Alto()
>>> obj.maker()
'Maruti'
>>> obj.power()
'800cc'
>>>
>>>
>>> class Swift(Alto):
    def new_features(self):
        return 'airbag, bluetooth'

>>> sw_obj = Swift()
>>> sw_obj.maker()
'Maruti'
>>> sw_obj.power()
'800cc'
>>> sw_obj.new_features()
'airbag, bluetooth'
>>>
>>> class Swift_newgen(Swift):
    def price(self):
        return '5L INR'
    def power(self):
        return '1200cc'

>>> ng_obj = Swift_newgen()
>>> ng_obj.price()
'5L INR'
>>> ng_obj.power()
'1200cc'
>>> ng_obj.maker()
'Maruti'
>>>

Note: Some of the examples in this tutorial are taken form official documentation/tutorial of python3. [See here] https://docs.python.org/3/tutorial/

Argument Passing

The python script name and additional arguments thereafter are turned into a list of string and assigned into argv variable in sys module.

  • When no script and no argument: sys.argv[0] is an empty string
  • When script name is given as -: sys.argv[0] is set to "-"
  • When -c or -m command is used: sys.argv[0] is set to -c or -m respectively

python -c 'print(hello world)'

Here -c stands for a python command Anything written after -c must be a valid python command

python -m pdb python-101.py

-m stands for module pdb stands for python debugger python-101.py is a file containing the python code

python -i python-101.py

-i means, python will run the program, python-101.py and dump you into interactive interpreter It helps in monitoring the variables at the end of the program.

To enter directly into python interpreter just type: python

Another way using python interpreter: Create a file named foo.py

The content of the file foo.py:

#!/usr/bin/env python

print("This is python-101")

There are two ways to run this file:

  • python foo.py
  • Make it executable chmod +x foo.py and run the executable ./foo.py

Modules

Standard library

sys

import sys

sys.platform

sys.path

os

import os

os.listdir('.')

os.path.getsize('index.html')

collections

python -m http.server

Django admin portal

install django

python -m pip install django

django-admin startproject library
django-admin startapp books

python manage.py makemigrations
python manage.py migrate

python manage.py createsuperuser

python manage.py runserver

Resources

People

Find other Python developers near you and get real time help from them. Python mailing lists

Need to conduct a python workshop in your institute? Contact Python Express

Books

Invent With Python

Think Python

Courses

https://www.edx.org/course/subject/computer-science/python

https://www.coursera.org/learn/python

https://www.edx.org/course/subject/computer-science/python

Material

https://github.com/ChillarAnand/python-101

https://docs.djangoproject.com/en/dev/intro/tutorial01/

https://pymbook.readthedocs.io/en/latest/