添加 python常用语法.md

python常用语法.md

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+```python
+# 列表
+range(0, 111, 2) ;  range(111, -1, -1)
+for i, num in enumerate(nums):
+nums.index(30)      nums.index(30, 2, 5)   # 在索引 2 到 5 的范围内查找值 30 的索引
+max_value = max(nums)
+max_index = nums.index(max_value)
+sorted(nums)      nums.sort()
+nums.reverse()
+res = [float('inf')] * 6
+[[0] * n for _ in range(m)]
+result.append(path[:])
+```
+```python
+# 栈
+stack = []
+stack.append(s)
+stack.pop()
+```
+```python
+# 字符串
+for c in t:   # t is str; c is char
+for c1, c2 in zip(s, t):  # s, t are str  
+for i, ch in enumerate(s):   # s: str
+ord(i) - ord("a")                
+chr(66)  #将 Unicode 编码值（整数）转换为对应的字符
+str(3)
+int("3")
+s[0:6]  # s is str 的切片语法
+repeated_s = s * 3
+s.upper()  #不会改变原字符串，如果想要修改，需要重新赋值
+s = "hello"    res=list(s)   ''.join(res)
+s = s1 + " " + s2
+```
+```python
+# 字典
+count = {};   count[s] = count.get(s, 0) + 1；  del count[s]
+count = collections.Counter(s1)
+dic = {}    
+count_dict = defaultdict(int)  # 使用 int，默认值为 0
+list_dict = defaultdict(list)  # 使用 list，默认值为空列表
+set_dict = defaultdict(set)  # 使用 set，默认值为空集合
+if s in dic:   # s is key
+dic["age"] = 26
+del dic["city"]
+for key in dic:
+for value in dic.values():
+for key, value in dic.items():
+dict(sorted(my_dict.items(), key=lambda item: item[0]))
+```
+```python
+# 队列
+from collections import deque
+d=deque([1, 2, 3, 4, 5])
+d.append(3)     d.appendleft(0)
+d.pop()      d.popleft()
+d[0]    d[-1]  # 查看左,右端元素
+```
+```python
+# 堆
+import heapq
+heap = [1, 5, 10]
+heapq.heapify(heap)
+heapq.heappush(heap, 1)
+heapq.heappop(heap)
+heapq.heappush(pri_que, (freq, key))  #小顶堆，大小序按照元组第一个元素freq
+```
+```python
+# 集合
+set = {1, 2, 3, 4}
+set = set([1, 2, 3, 4])
+set = set("aeiouAEIOU")
+set.add(3)
+set.update([1, 5])
+set.remove(2)
+set.pop()    随机删除一个元素
+set1.union(set2)
+if 3 in set:
+```
+```python
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+```
+```python
+import bisect
+bisect.bisect_right(nums, x)
+
+n, r = divmod(n, 10)
+a % b   a // b
+
+lambda x, y: int(x / y)
+
+from operator import add, sub, mul
+
+random.randint(1, 6)
+
+1 << 3  # 将数字 1 左移 3 位 = 8
+
+# 异或操作符 ^ 的规则是：相同为 0，相异为 1
+
+x & (x - 1)   # 消去x最后一位的1 
+x & (~ (x - 1))  # 获得最右边1开始至结尾
+
+```