Python Tricks

18. map(func, iter)

Executes the function func on all elements of the iterable iter.

>>> list(map(lambda x: x[0], ['red', 'green', 'blue']))
['r', 'g', 'b']

17. map(func, i1, …, ik)

Executes the function func on all k elements of the k iterables.

>>> list(map(lambda x,y: str(x) + ' ' + y + 's', [0, 2, 3], ['apple', 'orange', 'banana']))
['0 apples', '2 oranges', '3 bananas']

16. string.join(iter)

Concatenates iterable elements iter separated by string.

>>> ' marries '.join(list(['Alice', 'Bob']))
'Alice marries Bob'

15. filter(function, iterable)

Filters out elements in iterable for which function returns False (or 0).

>>> list(filter(lambda x: True if x > 17 else False, [1, 15, 17, 18, 19]))
[18, 19]

14. string.strip()

Removes leading and trailing whitespaces of string.

>>> print("   \n  \t   42  \t ".strip())
42

13. sorted(iter)

Sorts iterable iter in ascending order.

>>> sorted([8, 3, 2, 42, 5])
[2, 3, 5, 8, 42]

12. sorted(iter, key=key)

Sorts according to the key function in ascending order.

>>> sorted([8, 3, 2, 42, 5], key=lambda x: 0 if x==42 else x)
[42, 2, 3, 5, 8]

11. help(func)

Returns documentation of func.

>>> help(str.upper)
Help on method_descriptor:

upper(self, /)
    Return a copy of the string converted to uppercase.

10. zip(i1, i2, …)

Groups the k-th elements of iterators i1, i2, … together.

>>> list(zip(['Alice', 'Anna'], ['Bob', 'Jon', 'Frank'], ['Jason', 'Mike']))
[('Alice', 'Bob', 'Jason'), ('Anna', 'Jon', 'Mike')]

9. Unzip

Equal to: 1) unpack the zipped list, 2) zip the result.

>>> list(zip(*[('Alice', 'Bob', 'Jason'), ('Anna', 'Jon', 'Mike')]))
[('Alice', 'Anna'), ('Bob', 'Jon'), ('Jason', 'Mike')]

8. enumerate(iter)

Assigns a counter value to each element of the iterable iter.

>>> list(enumerate(['Alice', 'Bob', 'Jon']))
[(0, 'Alice'), (1, 'Bob'), (2, 'Jon')]

7. Start a web server

Want to share files between PC and phone? Run this command in PC’s shell.

is any port number 0–65535. Type :

in the phone’s browser. You can now browse the files in the PC directory.

python3 -m http.server <Port>

6. Read comic

Open the comic series xkcd in your web browser.

import antigravity

5. Zen of Python

Get valuable advice of how to write Pythonic code.

import this

4. Swapping numbers

Swapping variables is a breeze in Python. No offense, Java!

>>> a, b = 'Jane', 'Alice'
>>> a, b = b, a
>>> print(a, b)
Alice Jane

3. Unpacking arguments

Use a sequence as function arguments via asterisk operator *. Use a dictionary (key, value) via double asterisk operator **.

>>> def f(x, y, z):
...     return x + y*z
...
>>> f(*[1,3,4])
13
>>> f(**{'z':4, 'x':1, 'y':3})
13

2. Extended Unpacking

Use unpacking for multiple assignment feature in Python.

>>> a, *b = [1, 2, 3, 4, 5]
>>> print(a, b)
1 [2, 3, 4, 5]

1. Merge two dictionaries

Use unpacking to merge two dictionaries into a single one.

>>> x = {'Alice': 18}
>>> y = {'Bob': 27, 'Ann': 22}
>>> z = {**x, **y}
>>> print(z)
{'Alice': 18, 'Bob': 27, 'Ann': 22}