pylist

Python 库函数背诵树

Sequence (list, tuple)

Data management: non-slicing style

• 增
  • s.append(x)
  • s.extend(t) or s += t
  • s.insert(i, x)
• 删
  • s.pop([i])
  • s.remove(x)
  • s.clear()
• 查
  • summary
    • len(s)
    • max(s)
    • min(s)
  • existence
    • x in s
  • edit find
    • s.index(x[, i[, j]])
    • s.count(x)
• 改
  • s.reverse()

Data management: slicing Style

• 增
  • s[i:i] = t
    • append: s[len(s):len(s)] = [x]
    • extend: s[len(s):len(s)] = t
    • insert: s[i:i] = [x]
• 删
  • del s[i]
  • del s[i:j]
  • del s[i:j:k]
• 查
  • s[i]
  • s[i:j]
  • s[i:j:k] 越界自动停止
• 改
  • s[i] = x
  • s[i:j] = t 大小不需要一致
  • s[i,j,k] = t 大小必须一致

数学运算

• 加减乘除
  • a + b
  • shalow copy is not very often used

Set

数学运算

• 比较
  • a.isdisjoint(b)
  • a <= b
  • a < b
  • a >= b
• 加减乘除
  • a | b or
  • a & b and
  • a - b difference
  • a ^ b symetric difference

Data management

• 增
  • a.add(x)
• 删
  • a.remove(x) will raise error
  • a.discard(x) will not raise error if key not exist
  • a.pop()
  • a.clear()
• 查
  • summary
    • len(a)
    • max(a)
    • min(a)
  • existence
    • x in a
• 改
  • a |= b
  • a &= b
  • a -= b
  • a ^= b

Dict

Data management

• 增
  • d[key] = value
• 删
  • del d[key]
  • d.pop(key) return value
  • d.popitem() for distruction
  • a.clear()
• 查
  • iteration
    • d.items()
    • d.keys()
    • d.values()
    • iter(d) or iter(d.keys())
  • summary
    • len(d)
    • max(d) max key
    • min(d) min key
  • existence
    • key in d
• 改
  • d[key] = value
  • d1.update(d2)
  • reversed(d) 等同于 reversed(d.keys())

关于方向

• 3.7 和之后，dict 的 iterator 将会按照加入的顺序
  • 新加入才算
  • 修改不算
  • 删除后再加入算新加入
• 3.8 和之后，dict 可以 reverse
• set()没有方向

Operations with defaults

• d.get(key[, default])
• d.setdefault(key[, default])
  • d.setdefault(key, []).append(item)
  • 然而不能 d.setdefault(key, 0).add(1)，因为add不是inplace
• pop(key[, default])

deque

from collections import deque

• 增
  • q.append(x)
  • q.extend(t)
  • q.appendleft(x)
  • q.extendleft(t)
  • q.insert(i, x)
• 删
  • q.pop()
  • q.popleft()
  • q.remove(x) O(n) time complexity
• 查
  • q[i] q[0] and q[-1] peek
  • edit find
    • q.count(x)
    • q.index(x[, start[, stop]])
  • summary
    • len(q)
    • max(q)
    • min(q)
    • q.maxlen not a function
  • existence
    • x in q
• 改
  • q.rotate(n=1) O(n) time complexity
  • q.reverse()

heapq

from heapq import heapify, heappush, heappop
h = ***
heapify(h)
heappush(h, x)
x = heappop(h)
print(h[0]) # peek

max heap 的 负号位置

h = [-x for x in array]
heapify(h)
heappush(h, -x)
x = -heappop(h)
print(-h[0]) # peek

常用技巧

用for-else代替flag的使用

for item in container:
    if search_something(item):
        # Found it!
        process(item)
        break
else:
    # Didn't find anything..
    not_found_in_container()

Lambda function

fun1 = lambda x: -x * 10
print(fun1(1))

-10

same as

def fun2(x): return -x * 10
print(fun2(1))

-10

in sorting

a = [1, 4, -1, -3]
print(sorted(a))
print(sorted(a, key=fun1))
print(a)
print(a.sort(key=fun2))
print(a)

[-3, -1, 1, 4]
[4, 1, -1, -3]
[1, 4, -1, -3]
None
[4, 1, -1, -3]

a.sort() won’t return anything

ab = {'a':1, 'b':2, 'c': 4, 'd':3}
data = 'babdc'
data.sort()

      1 ab = {'a':1, 'b':2, 'c': 4, 'd':3}
      2 data = 'babdc'
----> 3 data.sort()

AttributeError: 'str' object has no attribute 'sort'

print(sorted(data))
print(sorted(data, key=lambda x: ab[x]))

['a', 'b', 'b', 'c', 'd']
['a', 'b', 'b', 'd', 'c']

Sort table

List 是可以按元素直接比较的，左边的权重高。 所以List of List 是可以直接sort的。 也可以取最值。 也可以heap。

详情

Example

• 209. First Unique Character in a String
• 612. K Closest Points

key in heap

heappush() and heappop does not have key attr. Need to define a __lt__() function for the same propose

from heapq import heappush, heappop
# self defined value
ab = {'a':1, 'b':2, 'c': 4, 'd':3}
# data
data = 'babdc'
# char class to define the comparison function
class char:
    def __init__(self, val):
        self.val = val
    def __lt__(self, other):
        if ab[self.val] < ab[other.val]:
            return True
        else:
            return False
# heap sort
h = []
for c in data:
    heappush(h, char(c))
ans = []
while h:
    ans.append(heappop(h).val)
print(ans)

['a', 'b', 'b', 'd', 'c']

Zip

zip 的操作是把同index放在一个tuple里，所以和转置息息相关。 注意zip的输出不是list，而是一个zip，可用作iter

使用zip函数转置list of tuples

# initializing list of tuples 
test_list = [('Akshat', 1), ('Bro', 2), ('is', 3), ('Placed', 4)] 
  
# Printing original list 
print ("Original list is : " + str(test_list)) 

# perform Unzipping 
res = list(zip(*test_list)) 
      
# Printing modified list  
print ("Modified list is : " + str(res)) 

Original list is : [('Akshat', 1), ('Bro', 2), ('is', 3), ('Placed', 4)]
Modified list is : [('Akshat', 'Bro', 'is', 'Placed'), (1, 2, 3, 4)]

注意事项

• // do floor operation to get the int number

  • >>> 11 // 4
    2
    >>> -11 // 4
    -3