流程控制
教材舉例
from sys import exit
def gold_room():
print "This room is full of gold. How much do you take?"
next = raw_input("> ")
if "0" in next or "1" in next:
how_much = int(next)
else:
dead("Man, learn to type a number.")
if how_much < 50:
print "Nice, you're not greedy, you win!"
exit(0)
else:
dead("You greedy bastard!")
def bear_room():
print "There is a beer here."
print "The bear has a bunch of honey."
print "The fat bear is in front of another door."
print "How are you going to move the bear?"
bear_moved = False
while True:
next = raw_input("> ")
if next == "take honey":
dead("The bear looks at you then slaps your face off.")
elif next == "taunt bear" and not bear_moved:
print "The bear has moved from the door. You can go through it now."
bear_moved = True
elif next == "taunt bear" and bear_moved:
dead("The bear gets pissed off and chews your leg off.")
elif next == "open door" and bear_moved:
gold_room()
else:
print "I got no idea what that means."
def cthulhu_room():
print "Here you see the great evil Cthulhu."
print "He, it, whatever stares at you and you go insane."
print "Do you flee for your life or eat your head?"
next = raw_input("> ")
if "flee" in next:
start()
elif "head" in next:
dead("Well that was tasty!")
else:
cthulhu_room()
def dead(why):
print why,"Good job!"
exit(0)
def start():
print "You are in a dark room."
print "There is a door to your right and left."
print "Which one do you take?"
next = raw_input("> ")
if next == "left":
bear_room()
elif next == "right":
cthulhu_room()
else:
dead("You stumble around the room until you starve.")
start()
上面是個(gè)小游戲哭廉，判斷用戶輸入決定流程走向慌洪，用戶是否通過熊的房間到達(dá)黃金屋只冻，不貪圖黃金順利完成任務(wù)株憾？簡(jiǎn)單的流程圖如下
上例中定義了５個(gè)函數(shù)
- start():開始
- bear_room():熊的房間
- gold_room():黃金屋
- cthulhu_room():邪神的房間
- dead():死亡退出
下面分析程序中的代碼
exit(0)
user@ubuntu:~/Documents$ python -m pydoc sys
.......
exit(...)
exit([status])
Exit the interpreter by raising SystemExit(status).
If the status is omitted or None, it defaults to zero (i.e., success).
If the status is an integer, it will be used as the system exit status.
If it is another kind of object, it will be printed and the system
exit status will be one (i.e., failure).
exit(0),退出解釋器蝙寨，同時(shí)拋出SystemExit exception
status可以為null，也可以是０嗤瞎，表示成功退出
如果status是一個(gè)整數(shù)墙歪，它將作為系統(tǒng)退出代碼，如果它是另外的對(duì)象贝奇，解釋器會(huì)將它打印出來虹菲，系統(tǒng)退出狀態(tài)碼將是１，表示異常退出掉瞳。
更多關(guān)于SystemExit
in
next = raw_input("> ")
if "0" in next or "1" in next:
how_much = int(next)
raw_input函數(shù)返回的是string類型毕源，屬于python的序列類型
Sequence Types — str
, unicode
, list
, tuple
, bytearray
, buffer
, xrange
'in'是一個(gè)比較運(yùn)算符(Comparisons operator)，所以可以用于真值判斷陕习。
比較運(yùn)算符還有
<
>
==
<=
>=
!=
<>
is
is not
in
not in
>,<,<>,==,!=,>=,<=通常用于比較兩個(gè)對(duì)象的值霎褐，兩個(gè)對(duì)象的類型可以不一樣，如果都是數(shù)字该镣，它們將被轉(zhuǎn)換成常用類型來比較冻璃，如果兩個(gè)不同對(duì)象來比較，通常結(jié)果都是不相等损合。
in和not in用于容器類型的成員判斷省艳，如if x in s，如果x是s的成員嫁审，將返回True拍埠，否則返回False.
is和is not用于對(duì)象身份的判斷，只有x和y是同一個(gè)對(duì)象時(shí)土居，x is y 返回True枣购，否則返回False.
