遍历循环
遍历某个结构形成的循环运行方式
for <循环变量> in <遍历结构>:
<语句块>
从遍历结构中逐一提取元素,放在循环变量中,每次循环所获得元素放入循环变量,并执行一次语句块
计数循环
for i in range(<次数>):
print(" ")
eg:
for i range(5)
print(i)
eg
for i range(5)
print"hello:",i)
for i in range(M, N, K):
print(i)
输出 ...:
1
2
3
4
5
特定次循环
for i in range(1, 6, 2):#表示1。。。5 跨度为2
...: print(i)
...:
1
3
5
字符串遍历循环
for c in s:
<语句块>
s是字符串,遍历字符串每个字符,产生循环
列表循环
for item in ls:
<语句块>
for item in [123, "py", 465]:
...: print(item, end=",")
...:
123,py,465,
文件循环遍历
for line in fi:
<语句块>
fi是一个文件标识符,遍历其每行,产生循环。
eg:
for line in fi:
print(line)
无限循环
由条件控制的循环运行方式:
while <条件>:
<语句块>
反复执行语句块,直到条件不满足时结束
In[8]: a=3
while a > 0:
...: a = a - 1
...: print(a)
...:
2
1
0
In[8]: a=3
while a > 0:
...: a = a + 1
...: print(a)
...: 无限循环点ctrl+c退出
循环控制保留字
break和continue保留字控制
break跳出并结束当前整个循环,执行循环后的语句
continue结束当次循环,继续执行后续次数循环
for c in "PYTHON": #字符串循环
...: if c == "T": #表示不打印T遍历其他字符串
...: continue
...: print(c, end="")
...:
PYHON
In[15]: for c in "PYTHON": #遇上保留字不循环其他
...: if c == "T":
...: break
...: print(c, end="")
PY
In[16]: s = "PYTHON"
while s !="": #判断s是否是空字符串
...: for c in s:
...: print(c, end="")
...: s = s[:-1] #每次去掉一个字符
...:
PYTHONPYTHOPYTHPYTPYP
In[18]: s = "PYTHON"
while s !="":
...: for c in s:
...: if c == "T": #跳出当次循环
...: break #一个break只能跳出一次循环
...: print(c, end="")
...: s = s[:-1]
...:
PYPYPYPYPYP
循环的高级用法
循环与else
当循环没有被break语句退出时,执行else语句块,else语句块作为“正常”完成循环的奖励,else用法与异常处理相似
In[20]: for c in "PYTHON":
...: if c == "T":
...: continue
...: print(c, end="")
...: else:
...: print("正常退出")
...:
PYHON正常退出
break语句
for c in "PYTHON":
...: if c == "T":
...: break
...: print(c, end="")
...: else:
...: print("正常退出")
...:
PY
在这里插入代码片