Python Basics

Whitespace Is Important



In [1]:

    
listOfNumbers = [1, 2, 3, 4, 5, 6]

for number in listOfNumbers:
    print number,
    if (number % 2 == 0):
        print "is even"
    else:
        print "is odd"
        
print "All done."









    



1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
All done.

Importing Modules



In [2]:

    
import numpy as np

A = np.random.normal(25.0, 5.0, 10)
print A









    



[ 18.9123893   24.82816779  29.44800245  27.80224122  28.49027554
  27.91360598  22.51271343  21.21800932  28.72865468  29.01646768]

Lists



In [3]:

    
x = [1, 2, 3, 4, 5, 6]
print len(x)



In [4]:

    
x[:3]









    Out[4]:





[1, 2, 3]



In [5]:

    
x[3:]









    Out[5]:





[4, 5, 6]



In [6]:

    
x[-2:]









    Out[6]:





[5, 6]



In [7]:

    
x.extend([7,8])
x









    Out[7]:





[1, 2, 3, 4, 5, 6, 7, 8]



In [8]:

    
x.append(9)
x









    Out[8]:





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



In [9]:

    
y = [10, 11, 12]
listOfLists = [x, y]
listOfLists









    Out[9]:





[[1, 2, 3, 4, 5, 6, 7, 8, 9], [10, 11, 12]]



In [10]:

    
y[1]









    Out[10]:





11



In [11]:

    
z = [3, 2, 1]
z.sort()
z









    Out[11]:





[1, 2, 3]



In [12]:

    
z.sort(reverse=True)
z









    Out[12]:





[3, 2, 1]

Tuples



In [13]:

    
#Tuples are just immutable lists. Use () instead of []
x = (1, 2, 3)
len(x)









    Out[13]:





3



In [14]:

    
y = (4, 5, 6)
y[2]









    Out[14]:





6



In [15]:

    
listOfTuples = [x, y]
listOfTuples









    Out[15]:





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



In [16]:

    
(age, income) = "32,120000".split(',')
print age
print income

Dictionaries



In [17]:

    
# Like a map or hash table in other languages
captains = {}
captains["Enterprise"] = "Kirk"
captains["Enterprise D"] = "Picard"
captains["Deep Space Nine"] = "Sisko"
captains["Voyager"] = "Janeway"

print captains["Voyager"]









    



Janeway



In [18]:

    
print captains.get("Enterprise")









    



Kirk



In [19]:

    
print captains.get("NX-01")









    



None



In [20]:

    
for ship in captains:
    print ship + ": " + captains[ship]









    



Voyager: Janeway
Deep Space Nine: Sisko
Enterprise D: Picard
Enterprise: Kirk

Functions



In [21]:

    
def SquareIt(x):
    return x * x

print SquareIt(2)



In [22]:

    
#You can pass functions around as parameters
def DoSomething(f, x):
    return f(x)

print DoSomething(SquareIt, 3)



In [23]:

    
#Lambda functions let you inline simple functions
print DoSomething(lambda x: x * x * x, 3)

Boolean Expressions



In [24]:

    
print 1 == 3









    



False



In [25]:

    
print (True or False)









    



True



In [26]:

    
print 1 is 3









    



False



In [27]:

    
if 1 is 3:
    print "How did that happen?"
elif 1 > 3:
    print "Yikes"
else:
    print "All is well with the world"









    



All is well with the world

Looping



In [28]:

    
for x in range(10):
    print x,









    



0 1 2 3 4 5 6 7 8 9



In [29]:

    
for x in range(10):
    if (x is 1):
        continue
    if (x > 5):
        break
    print x,



In [30]:

    
x = 0
while (x < 10):
    print x,
    x += 1









    



0 1 2 3 4 5 6 7 8 9

Activity

Write some code that creates a list of integers, loops through each element of the list, and only prints out even numbers!



In [ ]: