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
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¶
**