good practices

examples.py

'''
Defining dictionaries
'''

my_dict = {
    'key_1': 'notice the space after colon',
    'key_2': 'but not before the colon',
    'key_3': 'we are exactly 4 spaces indented'
}

'''
Function/Method definition. No space before open parenthesis,
underscores instead of camel case, 
no spaces before/after = in keyword args
wrapped at 79ish characters.
'''

def my_function(para1, para2, para3='foo', 
                para4='bar'):
    pass

'''
Function/Method invocation. You decide. Both are fine.
'''

results = my_function(para1, para2, para3='foo',
                      para4='bar')

results = my_function(
    para1,
    para2,
    para3='foo',
    para4='baar',
)

'''
Often "ors" can be better than long if statements
'''

my_long_var_email_name = request.user.email if request.user.email else "Unknown"
my_long_var_email_name = request.user.email or "Unkown"

'''
In Python. We are optimistic! We assume everything works 
and simply handle failure. Exceptions are better 
than if statements!
'''

if num.isdigit() and int(num) != 0:
  result = 1000 / num
else:
  result = 0

try:
  result = 1000 / int(num)
except ValueError, ZeroDivsionError:
  result = 0

'''
List comprehensions are awesome! In fact they are 4 times faster
than for loops. BUT DON'T USE THEM FOR COMPLEX LOGIC! 
'''

good = [i**2 for i in range(x) if i % 2]

bad = [x * y for x in range(10) for y in range(20) if not y % 2 and y > x]

'''
**** Do's and Don'ts ****
''''

if len(a) and a not in ('', [], {}, None, False, 0):
   print "DO THIS AND YOUR PULL REQUEST WILL BE REJECTED"

if a:
   print "Life can be so easy"

'''
Dictionaries are the heart of python. 
They are extremely powerful/fast and have 
all the built-in methods that one needs!
'''

if param in request.GET and request.GET['param'] not in ('', None):
    value = request.GET['param'] ### Don't do this
else:
    value = 0

value = request.GET.get('param', 0)

'''
If you can copy/paste code and change only minor things, 
then there is a better way to write it.
'''

### Bad
if SOMETHING:
    result = my_function(aaa=1, bbb=2, when_true=xyz)
else:
    result = my_function(aaa=1, bbb=2, when_true=abc)
    
### GOOD
params = {
    'aaa': 1,
    'bbb': 2,
    'when_true': xyz if SOMETHING else abc,
}
result = my_function(**params)

'''
Remember that in Python, variables are 
nothing more than pointers to memory locations!
What does b print in the last line here?
'''

### BAD
a = b = {}

### Good 
a = {}
b = {}

# Why?
a = b = {}
a[1] = 1
print b
{'1': 1}

'''
Remember that anything declared in the module scope
will only be evaluated once in the 
python 'compilation' (pyc) phase.
'''
 
def my_func(param1=datetime.now()):
    '''
    I don't work. The now() will only be 
    evaluated once!
    '''
    print param1

def my_func(param1=None):
    '''
    Need to make the evaluation of now() lazy.
    '''
    value = param1 or datetime.now()
    print value
   
'''
Python has single line conditional statements, don't exploit them.
What's a better way to write this?
'''

limit = int(kwargs['allowance']) if 'allowance' in kwargs and kwargs['allowance'] not in ('',0,None) else 0

try:
    limit = int(kwargs.get('allowance', 0))
except ValueError:
    limit = 0

'''
Don't use hardcode strings, integers etc in your code!
How long would it take to change the classifieds abbreviation 
from 'CL' to 'CLA'?
'''

### BAD
if a == 'hardcoded_string':
    # do stuff
    pass
elif b == 5:
    # do other stuff
    pass

### GOOD

CONSTANT_STRING = 'hardcoded_string'
MEANINGFUL_VAR = 5

if a == CONSTANT_STRING:
   # do stuff
   pass
elif b == MEANINGFUL_VAR:
   # do other stuff
   pass

'''
79 Characters? With a pinch of salt! 
Wrap when logical to do so. If you do wrap, don't use '\' 
this is very error prone! Use parenthesis instead.
'''
### BAD
if a and b and c and d and e \
   and f and g:
    pass

### GOOD
if (a and b and c and d and e
    and f and g):
    pass

'''
Strings can also conform to the 79 character rule
'''

bad_string = 'a really really really really really long string that is too long'

good_string = ('a really really '
               'really really really '
               'long string that is '
               'too long')

For CSS and HTML styles we could borrow from here: https://github.com/styleguide/