#!/usr/bin/env python
# coding: utf-8

# All the IPython Notebooks in this lecture series are available at https://github.com/rajathkumarmp/Python-Lectures

# #Control Flow Statements

# ##If

# if some_condition:
#     
#     algorithm

# In[1]:


x = 12
if x >10:
    print "Hello"


# ##If-else

# if some_condition:
#     
#     algorithm
#     
# else:
#     
#     algorithm

# In[2]:


x = 12
if x > 10:
    print "hello"
else:
    print "world"


# ##if-elif

# if some_condition:
#     
#     algorithm
# 
# elif some_condition:
#     
#     algorithm
# 
# else:
#     
#     algorithm

# In[3]:


x = 10
y = 12
if x > y:
    print "x>y"
elif x < y:
    print "x<y"
else:
    print "x=y"


# if statement inside a if statement or if-elif or if-else are called as nested if statements.

# In[4]:


x = 10
y = 12
if x > y:
    print "x>y"
elif x < y:
    print "x<y"
    if x==10:
        print "x=10"
    else:
        print "invalid"
else:
    print "x=y"


# ##Loops

# ###For

# for variable in something:
#     
#     algorithm

# In[5]:


for i in range(5):
    print i


# In the above example, i iterates over the 0,1,2,3,4. Every time it takes each value and executes the algorithm inside the loop. It is also possible to iterate over a nested list illustrated below.

# In[6]:


list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list1 in list_of_lists:
        print list1


# A use case of a nested for loop in this case would be,

# In[7]:


list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list1 in list_of_lists:
    for x in list1:
        print x


# ###While

# while some_condition:
#     
#     algorithm

# In[8]:


i = 1
while i < 3:
    print(i ** 2)
    i = i+1
print('Bye')


# ##Break

# As the name says. It is used to break out of a loop when a condition becomes true when executing the loop.

# In[9]:


for i in range(100):
    print i
    if i>=7:
        break


# ##Continue

# This continues the rest of the loop. Sometimes when a condition is satisfied there are chances of the loop getting terminated. This can be avoided using continue statement. 

# In[10]:


for i in range(10):
    if i>4:
        print "The end."
        continue
    elif i<7:
        print i


# ##List Comprehensions

# Python makes it simple to generate a required list with a single line of code using list comprehensions. For example If i need to generate multiples of say 27 I write the code using for loop as,

# In[11]:


res = []
for i in range(1,11):
    x = 27*i
    res.append(x)
print res


# Since you are generating another list altogether and that is what is required, List comprehensions is a more efficient way to solve this problem.

# In[12]:


[27*x for x in range(1,11)]


# That's it!. Only remember to enclose it in square brackets

# Understanding the code, The first bit of the code is always the algorithm and then leave a space and then write the necessary loop. But you might be wondering can nested loops be extended to list comprehensions? Yes you can.

# In[13]:


[27*x for x in range(1,20) if x<=10]


# Let me add one more loop to make you understand better, 

# In[14]:


[27*z for i in range(50) if i==27 for z in range(1,11)]