for 有截止条件的循环
基础语法：
for i in range(10);print(i)
举例说明：
version-1,循环10次猜年龄，猜对后退出。
AGE = 56 for i in range(10): guess_num = int(input("you guess num:")) if guess_num == AGE: print("Congratulations,you got it.") break elif guess_num > AGE: print("try smaller...") else: print("try bigger...")
version-2 循环10次猜年龄，猜对后退出，并且最多猜错3次，使用计数器递增限制循环次数。
AGE = 56 count = 0 for i in range(10): if count == 3: print("too many times...bye!") break guess_num = int(input("you guess num:")) if guess_num == AGE: print("Congratulations,you got it.") elif guess_num > AGE: print("try smaller...") else: print("try bigger...") count += 1
version-3 循环10次猜年龄，猜对后退出，并且最多猜错3次，不需要计数器递增直接使用i递增。
AGE = 56 for i in range(10): if i == 3: print("too many times...bye!") break guess_num = int(input("you guess num:")) if guess_num == AGE: print("Congratulations,you got it.") break elif guess_num > AGE: print("try smaller...") else: print("try bigger...")
version-4 每运行3次提示一次是否继续,计数器到达3时，根据提示重置计数器或退出
AGE = 56 count = 0 for i in range(10): if count == 3: user_confirm = input("do you want to keep guessing?").strip() if user_confirm == ‘y‘: count = 0 else: break guess_num = int(input("you guess num:")) if guess_num == AGE: print("Congratulations,you got it.") break elif guess_num > AGE: print("try smaller...") else: print("try bigger...") count += 1
continue
# 从1打印到10，走到5不打印 for i in range(10): if i == 5: pass else: print("loop ",i) for i in range(10): if i == 5: continue else: print("loop ",i)
break 跳出当前层的整个循环，continue 跳出当前层的本次循环，进入下一次循环
循环套循环
不打印内循环中的5
for i in range(10): print("out loop", i) for j in range(10): if j == 5: continue print(" inner loop", j)
外循环不打印5
for i in range(10): if i == 5: continue print("out loop",i) for j in range(10): print("inner loop", j)
外循环不打印5 ,内循环只打印到5
for i in range(10): if i == 5: continue print("out loop",i) for j in range(10): if j == 6: break print("inner loop", j)
while 循环
import time count = 0 t_start0 = time.time() while True: count += 1 if count == 10000000: break print("cost:", time.time() - t_start0, count) count = 0 t_start1 = time.time() while count < 10000000: count += 1 print("cost:", time.time() - t_start1, count)
三元运算
a = 2 b = 3 if a > b: c = a + b else: c = a - b print(c) -1 c = a + b if a > b else a - b print(c) -1
原文：http://www.cnblogs.com/Pangjn/p/6308546.html