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

# # Module 2
# 
# ## Video 7: Generating Lists
# **Python for the Energy Industry**
# 
# It's common to make a list by conditionally appending inside a loop. See this example of making a list of even numbers:

# In[1]:


evens = []

for i in range(11):
    if i % 2 == 0:
        evens.append(i)
        
print(evens)


# Here's another example, of finding the words in a list beginning with A:
# 
# *Note: strings can be treated in many ways as a list of characters - see below how we access the first letter of word as word[0]*

# In[2]:


words = ['AARDVARK','APPLE','ARROW','BARN','CACTUS']
a_words = []

for word in words:
    if word[0] == 'A':
        a_words.append(word)
        
print(a_words)


# This procedure is so common that there is a Python shorthand for it, called the 'list comprehension' which takes the form:
# 
# ``` new_list = [item for item in old_list if condition] ``` 
# 
# Here's how this looks for our even numbers example:

# In[3]:


evens = [i for i in range(11) if i % 2 == 0]

print(evens)


# You can also apply a function onto the item before storing it in the list. We will cover functions in more detail later, but here is a simple example:

# In[5]:


squares = [i**2 for i in range(10) if i % 2 == 0]

print(squares)


# ### Exercise
# 
# Try to write the list comprehension corresponding to our A words example.

# In[ ]: