Hello, Habr! I present to you the translation of the article "Bookmark this if you are new to Python (especially if you self-learn Python)" in two parts ( 1 , 2 ) with simple but useful tips and tricks in Python.

If, due to the boring quarantine life, you decide to dive into Python, congratulations. You are faced with the fastest growing programming language. I am sure that you already know some of the advantages of Python, such as its simplicity, ease of development, etc. These are also the main reasons I learned Python five years ago. I hope that you can learn Python more efficiently and enjoy this process, and for this I have prepared a list of simple but useful tricks and tips.

Clarification: I'm currently using Python 3.8 . If you encounter any problems while running my examples, please check to see if this is related to your version of Python.

Content

>>> a = 1
>>> b = 3
>>> a == 1
True
>>> a == 2
False
>>> a == b
False
>>> a > b
False
>>> a <= b
True
>>> if a <= b :
...     print('a is less than or equal to b')
...
a is less than or equal to b

. True False. if-else.

>>> def compare(a,b):
...     if a> b:
...             return a
...     else:
...             return b
...

return.

>>> def compare(a, b):
...     return a if a > b else b
...

/

>>> arr_list = [1,4,7]
>>> a = arr_list[0]
>>> b = arr_list[1]
>>> c = arr_list[2]

, :

>>> a, b, c = arr_list
>>> a
1
>>> b
4
>>> c
7

>>> arr_list = [1,4,7]
>>> result = []
>>> for i in arr_list:
...     result.append(i*2)
...
>>> result
[2, 8, 14]

>>> result = [x*2 for x in arr_list]
>>> result
[2, 8, 14]

zip

>>> a = [1,5,8]
>>> b = [3,4,7]
>>> result = []
>>> for i in range(len(a)):
...     result.append(a[i] if a[i] < b[i] else b[i])
...
>>> result
[1, 4, 7]

>>> result = [min(i) for i in zip(a,b)]
>>> result
[1, 4, 7]

lambda

>>> arr_list= [[1,4], [3,3], [5,7]]
>>> arr_list.sort(key=lambda x: x[1])
>>> arr_list
[[3, 3], [1, 4], [5, 7]]

filter, map

>>> arr_list = [-1, 1, 3, 5]
>>> result = []
>>> for i in arr_list:
...     if i > 0:
...             result.append(i**2)
...
>>> result
[1, 9, 25]

>>> result = list(map(lambda x: x**2, filter(lambda x: x > 0, arr_list)))
>>> result
[1, 9, 25]

: -, :)

Oleg Kapustin Kuldeep Pal.

>>> result = [i**2 for i in arr_list if i > 0]
>>> result
[1, 9, 25]

,

set , , .

>>> arr_list = [1,4,4,6,9]
>>> len(arr_list) == len(set(arr_list))
False

>>> pi = 3.14159
#  Python3.6
>>> print('The value of pi is {:.2f}'.format(pi))
The value of pi is 3.14

>>> a, b, c = 1,5,9
>>> print('a is {}; b is {}; c is {}'.format(a,b,c))
a is 1; b is 5; c is 9

#  Python3.6+
>>> print(f'The value of pi is {pi:.2f}')
The value of pi is 3.14
>>> pi
3.14159

>>> print(f'a is {a}; b is {b}; c is {c}')
a is 1; b is 5; c is 9

: PyFormat

enumerate

>>> arr_list = [1, 5, 9]
>>> for i in range(len(arr_list)):
...     print(f'Index: {i}; Value: {arr_list[i]}')
...
Index: 0; Value: 1
Index: 1; Value: 5
Index: 2; Value: 9

>>> for i, j in enumerate(arr_list):
...     print(f'Index: {i}; Value: {j}')
...
Index: 0; Value: 1
Index: 1; Value: 5
Index: 2; Value: 9

>>> arr_list = [1,4,6,8,10,11]
>>> a, *b, c = arr_list
>>> a
1
>>> b
[4, 6, 8, 10]
>>> c
11

itertools

>>> str_list = ['A', 'C', 'F']
>>> list(itertools.combinations(str_list,2))
[('A', 'C'), ('A', 'F'), ('C', 'F')]
>>> list(itertools.permutations(str_list,2))
[('A', 'C'), ('A', 'F'), ('C', 'A'), ('C', 'F'), ('F', 'A'), ('F', 'C')]

>>> a = 5
>>> b = 8
>>> temp = a
>>> a = b
>>> b = temp + a
>>> a
8
>>> b
13

. .

>>> a = 5
>>> b = 8
>>> a,b = b, a+b
>>> a
8
>>> b
13

(PS: ? !)

: Evaluation order

>>> str_list = ['This', 'is', 'WYFok']
>>> ' '.join(str_list)
'This is WYFok'

, , join. .

>>> ans_list = [3,6,9]
>>> 'The answer is '+','.join(map(str,ans_list))
'The answer is 3,6,9'

map , join .

: str.join, map

Underscore ()

, , for, :

>>> for i in range(3):
...     print('Hello')
...
Hello
Hello
Hello

, i for. i _ (). ( _ – , Python . , .)

>>> for _ in range(3):
...     print('Hello')
...
Hello
Hello
Hello

Dict.keys, Dict.values, Dict.items

>>> teacher_subject = {'Ben':'English','Maria':'Math','Steve':'Science'}
>>> teacher_subject.keys()
dict_keys(['Ben', 'Maria', 'Steve'])
>>> teacher_subject.values()
dict_values(['English', 'Math', 'Science'])
>>> teacher_subject.items()
dict_items([('Ben', 'English'), ('Maria', 'Math'), ('Steve', 'Science')])

keys values . items , . , .

>>> subject_teacher = {y:x for x,y in teacher_subject.items()}
>>> subject_teacher
{'English': 'Ben', 'Math': 'Maria', 'Science': 'Steve'}

: , .

(: zip )

>>> subject = ['English','Math','Scienc']
>>> teacher = ['Ben','Maria','Steve']
>>> subject_teacher = {f:v for f,v in zip(subject,teacher)}
>>> subject_teacher
{'English': 'Ben', 'Math': 'Maria', 'Scienc': 'Steve'}

: Mapping Types — dict

>>> a = {1,2,3}
>>> b = {1,2,3,4,5}
# a  b?
>>> a<=b
True
# b  a?
>>> a>=b
False
#  a  b 
>>> a.union(b)
{1, 2, 3, 4, 5}
#  a  b 
>>> a.intersection(b)
{1, 2, 3}
#  
#    a,    b 
>>> a.difference(b)
set()
#    b,    a
>>> b.difference(a)
{4, 5}

: Set

collections.Counter

, . Counter, .

>>> import collections
>>> arr_list = [1,1,1,1,2,2,2,3,3,5,5,5,7]
>>> c = collections.Counter(arr_list)
>>> c
Counter({1: 4, 2: 3, 5: 3, 3: 2, 7: 1})
>>> type(c)
<class 'collections.Counter'>
>>> c[1]
4
>>> c[6]
0
#    
>>> dict(c)
{1: 4, 2: 3, 3: 2, 5: 3, 7: 1}

Additional Information: collections.Counter

Conclusion

Although these tricks are fairly simple, they can help save time and simplify your code. I hope this article helped you figure out how to use the simple features of Python. Good training and code. See you next time.

Bookmark this article if you're new to Python (especially if you're learning Python yourself)