python_wiki:list_comprehensions [Owlbear Consulting

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====== List Comprehensions ======

**General Information**

List comprehensions are a way to create lists based on lists.

They cut out a step in which you would create an intermediate list just to create a new list.

**Checklist**
  * Python 2 or 3

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====== Usage ======

Using the code snippet. 
<code bash>
chmod +x list-comp.py
./list-comp.py
 
# Example output
('The tuple is: ', ('centos', 'ubuntu', 'fedora', 'windows', 'arch', 'freebsd'))
('The nix os list is: ', ['centos', 'ubuntu', 'fedora', 'arch', 'freebsd'])
</code>

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====== The Code ======

**List Comprehension Syntax**
<code python>
new_list = [x for x in iterable if filter]
</code>

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**List Comprehension Example**
<code python list-comp.py>
#!/usr/bin/python

# Tuple with a list of OS's
my_tuple = ('centos', 'ubuntu', 'fedora', 'windows', 'arch', 'freebsd')

# Create a new list based off of the tuple, exclude 'windows'
nix_os = [entry for entry in my_tuple if entry != 'windows']

print("The tuple is: ", my_tuple)
print("The nix os list is: ", nix_os)
</code>

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The long way **without list comprehensions** of the above code is
<code python>
#!/usr/bin/python

# Tuple with a list of OS's
my_tuple = ('centos', 'ubuntu', 'fedora', 'windows', 'arch', 'freebsd')

# Create a new list based off of the tuple, exclude 'windows'
# This time, do not use a list comprehension
nix_os = []
for entry in my_tuple:
  if entry != 'windows':
    nix_os.append(entry)

print("The tuple is: ", my_tuple)
print("The nix os list is: ", nix_os)
</code>

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