2 Introduction to Python

A series of commands to introduce beginners to Python.

Does it work?



In [1]:

    
print('Hello, world!')









    



Hello, world!



In [2]:

    
2 + 2









    Out[2]:





4



In [3]:

    
import numpy

Define Variables



In [4]:

    
a_integer = 5



In [5]:

    
a_float = 1.41421356237



In [6]:

    
a_integer + a_float









    Out[6]:





6.41421356237



In [7]:

    
a_number = a_integer + a_float



In [8]:

    
print(a_number)









    



6.41421356237



In [9]:

    
a_string = 'How you doing, world?'



In [10]:

    
print(a_string)









    



How you doing, world?



In [11]:

    
a_integer + a_string









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-11-bd0cee6f46e6> in <module>()
----> 1 a_integer + a_string

TypeError: unsupported operand type(s) for +: 'int' and 'str'



In [12]:

    
print(a_integer, a_string)









    



5 How you doing, world?



In [13]:

    
str(a_integer) + a_string









    Out[13]:





'5How you doing, world?'



In [14]:

    
a_float = 3.1417



In [15]:

    
print(a_float)



In [16]:

    
who









    



a_float	 a_integer	 a_number	 a_string	 numpy



In [17]:

    
# This is a comment



In [18]:

    
"""This is a multi-
line comment"""









    Out[18]:





'This is a multi-\nline comment'

Comments are handy to temporarily turn some lines on or off and to document Python files. In Jupyter notebooks using markdown cells gives more control.

Mathematical Operations



In [19]:

    
9/3









    Out[19]:





3.0



In [20]:

    
9/4.0









    Out[20]:





2.25



In [21]:

    
9%4









    Out[21]:





1



In [22]:

    
2**6









    Out[22]:





64



In [23]:

    
64**(0.5)









    Out[23]:





8.0

Logical Operations



In [24]:

    
a = True
b = False



In [25]:

    
2 == 2.0









    Out[25]:





True



In [26]:

    
2 != 2.000001









    Out[26]:





True



In [27]:

    
6 > 10









    Out[27]:





False



In [28]:

    
if 6 > 4:
    print('Six is greater than four!')









    



Six is greater than four!



In [29]:

    
if 6 > 10:
    print('Six is greater than ten!')
else:
    print('Six is not greater than ten!')









    



Six is not greater than ten!



In [30]:

    
a = 25
if a%2 == 0:
    print('This number is even!')
elif a%3 == 0:
    print('This number is divisable by three!')
elif a%5 == 0:
    print('This number is divisable by five!')
else:
    print(str(a) + ' is not divisable by 2, 3 or 5!')









    



This number is divisable by five!



In [31]:

    
b = 0
while b < 5:
    print(b)
    b = b + 1



In [32]:

    
b









    Out[32]:





5



In [33]:

    
while True:
    pass









    



---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-33-b7133701d76c> in <module>()
      1 while True:
----> 2     pass

KeyboardInterrupt:



In [34]:

    
a = 25
b = 1
c = 2
while b != 0:
    b = a%c
    if b == 0:
        print(str(a) + ' is divisable by ' + str(c))
    else:
        c += 1









    



25 is divisable by 5

Exercise: Can you rework this code so that you can test if a number is prime (so only it and 1 divides it)



In [35]:

    
a = 29
b = 1
c = 2
while b != 0:
    b = a%c
    if a == c:
        print(str(a) + ' is a prime number.')
    elif b == 0:
        print(str(a) + ' is divisable by ' + str(c))
    else:
        c += 1









    



29 is a prime number.