python入门 -- 学习笔记3

习题21：函数可以返回东西

过程解析：

1、定义函数：如def add(形参)函数

2、调用函数： add(实参)    别忘记加()

3、在函数调用的时候将实参的值传给形参，代入到函数中进行计算，return 关键字将函数计算的结果再返回给调用它的地方

代码：

def add(a, b):
　　print "ADDING %d + %d" % (a, b)
　　return a + b

def subtract(a, b):
　　print "SUBTRACTING %d - %d" % (a, b)
　　return a - b

def multiply(a, b):
　　print "MULTIPLYING %d * %d" % (a, b)
　　return a * b

def divide(a, b):
　　print "DIVIDING %d / %d" % (a, b)
　　return a / b

print "Let's do some math with just functions!"

age = add(30, 5)
height = subtract(78, 4)
weight = multiply(90, 2)
iq = divide(100, 2)

print "Age: %d, Height: %d, Weight: %d, IQ: %d" % (age, height, weight, iq)

# A puzzle for the extra credit, type it in anyway.
print "Here is a puzzle."

what = add(age, subtract(height, multiply(weight, divide(iq, 2))))

print "That becomes: ", what, "Can you do it by hand?"

结果：

习题24：更多练习

代码：

print "Let's practice everything"
print "You\'d need to know \'bout escapes with \\ that do \n newlines and \t tabs."

poem = '''
　　\tThe lovely world
　　with logic so firmly planted
　　cannot discern \n the needs of love
　　nor comprehend passion from intuition
　　and requires an explanation
　　\n\t\twhere there is none.
'''

print "---------------------"
print poem
print "---------------------"

five = 10 - 2 + 3 - 6
print "This should be five: %s" % five

def secret_formuls(started):
　　jelly_beans = started * 500
　　jars = jelly_beans / 1000
　　crates = jars / 100
　　return jelly_beans, jars, crates

start_point = 10000
beans, jars, crates = secret_formuls(start_point)

print "With a starting point of: %d" % start_point
print "We'd have %d beans, %d jars, and %d crates." % (beans, jars, crates)

start_point = start_point / 10

print "We can also do that this way:"
print "We'd have %d beans, %d jars, and %d crates." % secret_formuls(start_point)

结果：

习题27：记住逻辑关系

逻辑术语：

　　and   与

　　or   或

　　not   非

　　!= (not equal)   不等于

　　== (equal)   等于

　　>= (greater-than-equal)   大于等于

　　<= (less-than-equal)   小于等于

　　True   真

　　False   假

真值表：

NOT

not False    True
not True    False

OR
True or False   True
True or True   True
False or True   True
False or False   False

AND
True and False   False
True and True    True
False and True   False
False and False   False

NOT OR
not (True or False)   False
not (True or True)   False
not (False or True)   False
not (False or False)   True

NOT AND
not (True and False)   True
not (True and True)   False
not (False and True)   True
not (False and False)   True

!= 
1 != 0    True
1 != 1    False
0 != 1    True
0 != 0    False

==
1 == 0    False
1 == 1    True
0 == 1    False
0 == 0    True

习题29：如果（if）

格式：

　　if 布尔表达式  : （“:”后跟一个代码块，每个语句都有4个空格的缩进）

　　　　语句（如果布尔表达式结果为真，则执行该语句，否则跳过该语句）

代码：

people = 20 
cats = 30
dogs = 15

if people < cats:
　　print "Too many cats! The world is doomed!"

if people > cats:
　　print "Not many cats! The world is saved!"

if people < dogs:
　　print "The world is drooled on!"

if people > dogs:
　　print "The world id dry!"

dogs += 5

if people >= dogs:
　　print "People are greater than or equal to dogs."

if people <= dogs:
　　print "people are less than or equal to dogs."

if people == dogs:
　　print "People are dogs."

结果：

习题30：Else 和 If

代码：

people = 20 
cars = 40
buses = 15

if cars > people:
　　print "We should take the cars."

elif cars < people:
　　print "We should not take the cars."
else:
　　print "We can't decide."

if buses > cars:
　　print "That's too many buses."
elif buses < cars:
　　print "Maybe we could take the buses."
else:
　　print "We still can't decide."

if people > buses:
　　print "Alright, let's just take the buses."
else:
　　print "Fine, let's stay home then."

结果：

习题31：作出决定

代码：

print "You enter a dark room with two doors. Do you go through door #1 or door #2?"

door = raw_input("> ")
if door == "1":
　　print "There's a giant bear here eating a cheese cake. What do you do?"
　　print "1. Take the cake."
　　print "2. Scream at the bear."

　　bear = raw_input("> ")

　　if bear == "1":
　　　　print "The bear eats your face off. Good job!"
　　elif bear =="2":
　　　　print "The bear eats your legs off. Good job!"
　　else:
　　　　print "Well, doing %s is probablt better. Bear runs away." % bear

elif door == "2":
　　print "You stare into the endless abyss at Cthulhu's retina."
　　print "1. Blueberries."
　　print "2. Yellow jacket clothespins."
　　print "3. Understanding revolvers yelling melodies."

　　insanity = raw_input("> ")

　　if insanity == "1" or insanity == "2":
　　　　print "Your body survives powered by a mind of jello. Good job!"
　　else:
　　　　print "The insanity rots your eyes into a pool of muck. Good job!"

else:

　　print "You stumble around and fall on a knife and die. Good job!"

结果：

习题32：循环与列表

-- 使用刘表元素所在的位置数（基数）访问列表元素，更多列表相关可上网搜索

代码：

the_count = [1, 2, 3, 4, 5]
fruits = ['apples', 'oranges', 'pears', 'apricots']
change = [1, 'pennies', 2, 'dimes', 3, 'quarters']

# this first kind of for-loop goes through a list
for number in the_count:
　　print "This is count %d" % number

# same as above
for fruit in fruits:
　　print "A fruit of type: %s" % fruit

# alse we can go through mixes lists too
# notice we have to use %r since we don't know what's in it
for i in change:
　　print "I got %r" % i

# we can also build lists, first start with an empty one
elements = []

# then use the range function to do 0 to 5 counts
for i in range(1, 6):
　　print "Adding %d to the list." % i
# append is a function that lists understand
　　elements.append(i)

# now we can print them out too
for i in elements:
　　print "Element was: %d" % i

结果：

习题33：While循环 --  尽量少用，大部分时候用for循环

代码：

i = 0
numbers = []

while i < 6:
　　print "At the top i is %d" % i
　　numbers.append(i)

　　i += 1
　　print "Numbers now: ", numbers
　　print "At the bottom i is %d" % i

print "The numbers: "

for num in numbers:
print num

结果：

习题35：分支与函数

代码：

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 bear 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 "Hear 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()

结果：（路径之一）

习题36：设计与调试

If 语句的规则

1. 每一个“if 语句”必须包含一个 else.
2. 如果这个 else 永远都不应该被执行到，因为它本身没有任何意义，那你必须在 else 语句后面
使用一个叫做 die 的函数，让它打印出错误信息并且死给你看，这和上一节的习题类似，这样你
可以找到很多的错误。
3. “if 语句”的嵌套不要超过 2 层，最好尽量保持只有 1 层。 这意味着如果你在 if 里边又有了
一个 if，那你就需要把第二个 if 移到另一个函数里面。
4. 将“if 语句”当做段落来对待，其中的每一个 if, elif, else 组合就跟一个段落的句子组
合一样。在这种组合的最前面和最后面留一个空行以作区分。
5. 你的布尔测试应该很简单，如果它们很复杂的话，你需要将它们的运算事先放到一个变量里，并
且为变量取一个好名字。

循环的规则

1. 只有在循环永不停止时使用“while 循环”，这意味着你可能永远都用不到。这条只有 Python
中成立，其他的语言另当别论。
2. 其他类型的循环都使用“for 循环”，尤其是在循环的对象数量固定或者有限的情况下。

调试(debug)的小技巧

1. 不要使用 “debugger”。 Debugger 所作的相当于对病人的全身扫描。你并不会得到某方面的
有用信息，而且你会发现它输出的信息态度，而且大部分没有用，或者只会让你更困惑。
2. 最好的调试程序的方法是使用 print 在各个你想要检查的关键环节将关键变量打印出来，从而
检查哪里是否有错。
3. 让程序一部分一部分地运行起来。不要等一个很长的脚本写完后才去运行它。写一点，运行一点，
再修改一点。

习题37：复习各种符号

Keywords（关键字）

• and
• del
• from
• not
• while
• as
• elif
• global
• or
• with
• assert
• else
• if
• pass
• yield
• break
• except
• import
• print
• class
• exec
• in
• raise
• continue
• finally
• is
• return
• def
• for
• lambda
• try

数据类型

• True
• False
• None
• strings
• numbers
• floats
• lists

字符串转义序列(Escape Sequences)

• \\
• \'
• \"
• \a
• \b
• \f
• \n
• \r
• \t
• \v

字符串格式化(String Formats)

• %d
• %i
• %o
• %u
• %x
• %X
• %e
• %E
• %f
• %F
• %g
• %G
• %c
• %r
• %s
• %%

操作符号

• +
• -
• *
• **
• /
• //
• %
• <
• >
• <=
• >=
• ==
• !=
• <>
• ( )
• [ ]
• { }
• @
• ,
• :
• .
• =
• ;
• +=
• -=
• *=
• /=
• //=
• %=
• **=