根据《Python编程入门经典》(James Payne著,张春晖译)整理。
比较两个值是否相等。
>>> 1 == 1 True >>> 1 == -1 False >>> a = ["a", "b", "c"] >>> b = ["a", "b", "cd"] >>> a == b False
比较两个值是否不相等。
>>> 1 !=1 False >>> 1 != 2 True
比较两个值大小。
>>> 3 > 2 True
取反。
>>> not True False >>> not False True
和运算。
>>> 1 == 1 and 2 == 2 True >>> 1 !=1 and 2 == 2 False
或运算。
>>> 1!=1 or 2 == 2 True >>> 1 != 1 or 2 != 2 False
if
>>> if 2 > 1: ... print("yes") ... yes
嵌套
>>> omelet_ingredients = {"egg":2, "mushroom":5, "pepper":1, "cheese":1, "milk":1} >>> fridge_contents = {"egg":10, "mushroom":20, "pepper":3, "cheese":3, "tomato":4, "milk":15} >>> if(omelet_ingredients["egg"] < fridge_contents["egg"]): ... have_ingredients[0] = True ... have_ingredients.append("egg") ... >>> print(have_ingredients) [True, 'egg'] >>> if(omelet_ingredients["mushroom"] < fridge_contents["mushroom"]): ... if(have_ingredients[0] == False): ... have_ingredients[0] = True ... have_ingredients.append("mushroom") ... >>> print(have_ingredients) [True, 'egg', 'mushroom']
循环
while
>>> i = 10 >>> while i > 0: ... print(i) ... i = i-1 ... 10 9 8 7 6 5 4 3 2 1
for
>>> for i in range(5): ... print(i) ... 0 1 2 3 4
>>> for i in range(10, 0, -2): ... print(i) ... 10 8 6 4 2
break
终止循环。
>>> for i in range(10, 0, -1): ... print(i) ... if i == 5: ... break ... 10 9 8 7 6 5
continue
跳过当前循环。
>>> i = 10 >>> while i > 0: ... i = i - 1 ... if i == 3: ... continue ... print(i) ... 9 8 7 6 5 4 2 1 0