Best Coding Practices¶

Here we list the best python coding practices which are relatively less known

Loops¶

When using a for loop use enumerate function instead of incrementing a counter:

for ix, item in enumerate(my_list):
    # ix represents index. It acts as a counter
    # item contains the value.

When traversing through multiple lists of same size use zip function

for itm_a, itm_b in zip(list_a, list_b):
    # itm_a contains the value of list_a
    # itm_b contains the value of list_b

If you want to loop backwards, use reversed function:

for color in reversed(colors):
    print(color)

Suppose you want to use a for loop with break statement. You could check whether the loop ran completely by using an else statement:

for item in my_list:
    if item == 'something':
        print("Item found")
        break

# This else acts like if no-break occured. No need to use extra variables.
else:
    print("The loop did not break")

Dictionaries¶

Suppose you wanted to obtain the value corresponding to a key in a dictionary, use:

# No error even if the key is not present in the dictionary.
my_val = my_dict.get('my_key', 'my_default_val')

You could contruct a dictionary from pairs using zip and dict constructor:

names = ['nikhil', 'aparnna']
ages = ['29', '24']

d = dict(zip(names, ages))

Counting with dictionary. Suppose you had a list with repeating items and you had to count the number of occurrences of each item. The simplest way is to use the following:
```
colors = ['red', 'green', 'red', 'blue', 'green', 'red']
d = {}
for color in colors:
    d[color] = d.get(color, 0) + 1
```

We could use defaultdict instead of plain dict from python if we know the type of values being stored. Suppose I know that my values are integers, like the code above, I could write the following code:

from collections import defaultdict
colors = ['red', 'green', 'red', 'blue', 'green', 'red']
d = defaultdict(int) # default value of int is 0
for color in colors:
    d[color] += 1 # defaultdict never raises a KeyError

# ice_cream = defaultdict(lambda: 'Vanilla') <-- Assigning a function object to the defaultdict

You can also group a set of items in a list using a defaultdict. For instance:

from collections import defaultdict
names = ['nikhil', 'aparnna', 'kameswari', 'vamsi', 'prasad', 'p.p.rao']
d = defaultdict(list) # The default value is an empty list

for name in names:
    key = len(name) # Grouping the names based on their length
    d[key].append(name)

Miscellaneous¶

To exchange the values of two variables, do not use a third temporary variable. Instead use:
```
# This is clean and easy to understand
x, y = y, x
```

You can use an else statement even with try and except to execute statements there were no exceptions. Similarly, you can use finally to execute statements regardless of whether an exception occurred or not:

try:
    print(int('x'))
except:
    print('Conversion Failed')

# If No-Except
else:
    print('Conversion successful')

# Always execute this statement.
finally:
    print('Done')

You can also use only try and finally as follows:

try:
    f = open('my_file.txt')
    # Contains the clean up code which needs to be executed even if an exception occurred.
finally:
    f.close()

While reading a text file we can use with statement with context, without having to close it manually:
```
with open('my_file.txt') as f:
    for line in f:
        print(line)
```

Always clarify function calls with keyword arguments:

# Bad way
twitter_search('@obama', False, 20, True)

# Good way
twitter_search('@obama', retweets=False, numtweets=20, popular=True)

Always, return NamedTuple instead of plain Tuple as it is more informative:

# Bad way
def get_body_stats():
    return (70, 6)

# Good way
from collections import namedtuple
def get_body_stats():
    BodyStats = namedTuple('BodyStats', ['weight', 'height'])
    return BodyStats(70, 6)

For generating documentation from your python code see the `sphinx for python documentation blog<https://gisellezeno.com/tutorials/sphinx-for-python-documentation.html>`_.