Python Fundamental

Posted by Ray on December 19, 2023

string.strip()

### Usage 1. remove all empty 2. it allows arguments e.g. \'abbabbacdef\'.strip(\'ab\'). it remove both `a` and `b` (the sequence does not matter) ### exampls ```python string.strip(" aaa \n ") ```

calculate total of 1\~100 #card

### Usage 1. sum and range ### exampls ```python sum(range(1, 100)) ```

sum(range(1, 100))

remove 'key' from dict #card

del dict['key']

merge two dict, dict1 and dict2 #card

dict1.update(dict2)

deduplicate from a list #card

use set

list(set(mylist)) **

*args and **kwargs #card

args: positional arguments

kwargs: kv arguments (dict)

What is dectorator #card

a function return function and the argument is a function

difference between __init__ and __new__ #card

__init__ 是初始化方法,创建对象后,就立刻被默认调用了,可接收参数, first arg is self

__new__ take cls which is current class. It need to return the new class

with #card

it implement finally: file.close()

[1,2,3,4,5] -> [1,4,9,16,25] #card

list comprehension: [i*i for i in l]

map: map(lambda x: x*x, [1,2,3,4,5])

s='abccba' deduplicate and sort #card

''.join(sorted(list(set(s)))

What is difference between remove , discard, del and pop when remove a element from a list #card

remove(v) remove first element with value v

del l[2] remove element from l at pos 2

pop(idx=-1)

discard does not raise exception when key not existed

Sort a dict based on key #card

sorted(dict.items(), key=lambda i: i[0], reverse=False)

find all odd number in a list #card

list comprehension [i for i in l if i%2==1]

filter(): filter(lambda i i%2==1, [1,2,3,4])

merge two list l1, l2 and sort #card

l1.extend(l2); sorted(l1)

a=[[1, 2], [3, 4]] -> [1,2,3,4] #card

two steps [ j for i in a for j in i ] ~for i in a ~ each i is [1, 2], [3, 4]; for j in i -> 1,2 3, 4

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