

In [1]:

    
print('hello world')









    



hello world

This was our first Python command.

Basic Python Explorations

There are some minor differences between Python2 and Python3. Let us consider an example:



In [3]:

    
# This is an inline comment: Python3
print('hello world')

# Python2
print 'hello world'









    



  File "<ipython-input-3-7d0e8552180e>", line 5
    print 'hello world'
                      ^
SyntaxError: invalid syntax

Basic Types

We now look at the different types of objects that Python offers: floats, integers, booleans, lists, dictionaries, etc.



In [5]:

    
1 * 1.0
a = 3
type(a)









    Out[5]:





builtins.int



In [6]:

    
b = 3 > 5
print(b), type(b)









    



False






    Out[6]:





(None, builtins.bool)

Let us now turn to containers: lists, dictionaries.



In [7]:

    
L = ['red', 'blue', 'green', 'black', 'white']
print(L)









    



['red', 'blue', 'green', 'black', 'white']



In [10]:

    
L[1], L[3:], L[3:15]









    Out[10]:





('blue', ['black', 'white'], ['black', 'white'])

Lists are mutable objects, i.e. they can be changed.



In [11]:

    
L[1] = 'yellow'
print(L)









    



['red', 'yellow', 'green', 'black', 'white']

What is an example of an immutable object?



In [12]:

    
T = ('red', 'black')
T[1] = 'yellow'









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-12-34af57d15608> in <module>()
      1 T = ('red', 'black')
----> 2 T[1] = 'yellow'

TypeError: 'tuple' object does not support item assignment

Let us now turn to the distinction between independent copies and references to objects.



In [17]:

    
print(L)
G = L
print(G,L)

# But now:
L[1] = 'blue'
print(G,L)

# Let us now create an independent copy:
G = L[:]
print('Independent: ', G, L)
L[1] = 'yellow'
print('Independent: ', G, L)









    



['red', 'blue', 'green', 'black', 'white']
['red', 'blue', 'green', 'black', 'white'] ['red', 'blue', 'green', 'black', 'white']
['red', 'blue', 'green', 'black', 'white'] ['red', 'blue', 'green', 'black', 'white']
Independent:  ['red', 'blue', 'green', 'black', 'white'] ['red', 'blue', 'green', 'black', 'white']
Independent:  ['red', 'blue', 'green', 'black', 'white'] ['red', 'yellow', 'green', 'black', 'white']

Miscellaneous

Python Resources

Formatting



In [2]:

    
import urllib; from IPython.core.display import HTML
HTML(urllib.urlopen('http://bit.ly/1K5apRH').read())









    Out[2]: