author：headsen chen

date：2018-06-01 15:39:26

习题17，文件的更多操作

[root@localhost py]# echo 1234567890 >cc.txt

[root@localhost py]# cat file3.py

#!/usr/bin/env pythonfromsys import argvfromos.path import exists

script,from_file,to_file=argv

print"Copying from %s to %s" %(from_file,to_file)

# we coulddo these two on one line too,how?input=open(from_file)

indata=input.read()

print"The input file is %d bytes long"%len(indata)

print"Does the output file exist? %r"%exists(to_file)

print"Ready,hit RETURN to continue, CTRL-C to abort."raw_input()

output= open(to_file,'w')

output.write(indata)

print"Alright,all done."output.close()

input.close()

[root@localhost py]#python file3.py cc.txt dd.txt

Copying fromcc.txt to dd.txt

The input fileis 11bytes long

Does the output file exist? True

Ready,hit RETURN tocontinue, CTRL-C to abort.

Alright,all done.

检验新生成的dd.txt文件：

[root@localhost py]# cat dd.txt

1234567890

这里不过dd.txt是否存在，若存在：清空然后复制cc.txt的内容过来，若不存在dd.txt文件就创建dd.txt文件并复制内容过来

补充：exists这个命令将文件名字符串作为参数，如果文件存在的话，它将返回 True，否则将返回 False。

习题18：函数 ---> 理解成“迷你脚本”

函数可以做三样事情：

1.它们给代码片段命名，就跟“变量”给字符串和数字命名一样。

2.它们可以接受参数，就跟你的脚本接受 argv 一样。

3.通过使用 #1 和 #2，它们可以让你创建“微型脚本”或者“小命令”。

[root@localhost py]#cat func1.py#!/usr/bin/env python

#this is like you scripts with argv

def print_two(*args):

arg1,arg2=argsprint "arg1:%r,arg2:%r" %(arg1,arg2)#ok,that *args is actually pointless,we can just do this

defprint_two_again(arg1,arg2):print "arg1:%r,arg2:%r" %(arg1,arg2)#this just takes one argument

defprint_one(arg1):print "arg1:%r"%arg1#this one takes no arguments

defprint_none():print "I got nothing."print_two('zen','hello')

print_two_again('ZEN','HELLO')

print_one('First!')

print_none()

[root@localhost py]#python func1.py

arg1:'zen',arg2:'hello'arg1:'ZEN',arg2:'HELLO'arg1:'First!'I got nothing.

习题 19: 函数和变量

[root@localhost py]#cat func2.py#!/usr/bin/env python

defcheese_and_crackers(cheese_count, boxes_of_crackers):print "You have %d cheeses!" %cheese_countprint "You have %d boxes of crackers!" %boxes_of_crackersprint "Man that's enough for a party!"

print "Get a blanket.\n"

print "We can just give the function numbers directly:"cheese_and_crackers(20, 30)print "OR, we can use variables from our script:"amount_of_cheese= 10amount_of_crackers= 50cheese_and_crackers(amount_of_cheese, amount_of_crackers)print "We can even do math inside too:"cheese_and_crackers(10 + 20, 5 + 6)print "And we can combine the two, variables and math:"cheese_and_crackers(amount_of_cheese+ 100, amount_of_crackers + 1000)

[root@localhost py]#python func2.py

We can just give the function numbers directly:

You have20cheeses!

You have30boxes of crackers!

Man that's enough for a party!

Get a blanket.

OR, we can use variablesfromour script:

You have10cheeses!

You have50boxes of crackers!

Man that's enough for a party!

Get a blanket.

We can even do math inside too:

You have30cheeses!

You have11boxes of crackers!

Man that's enough for a party!

Get a blanket.

And we can combine the two, variablesandmath:

You have110cheeses!

You have1050boxes of crackers!

Man that's enough for a party!

Get a blanket.

习题 20: 函数和文件

[root@localhost py]#cat aa.txt

aaaaaa

bbbbbb

cccccc

[root@localhost py]#cat func-file.py

#!/usr/bin/env python

from sys importargv

script, input_file=argvdefprint_all(f):printf.read()defrewind(f):

f.seek(0)defprint_a_line(line_count, f):printline_count, f.readline()

current_file=open(input_file)print "First let's print the whole file:\n"print_all(current_file)print "Now let's rewind, kind of like a tape."rewind(current_file)print "Let's print three lines:"current_line= 1print_a_line(current_line, current_file)

current_line= current_line + 1print_a_line(current_line, current_file)

current_line= current_line + 1print_a_line(current_line, current_file)

[root@localhost py]#python func-file.py aa.txt

First let's print the whole file:

aaaaaa

bbbbbb

cccccc

Now let's rewind, kind of like a tape.

Let's print three lines:

1aaaaaa2bbbbbb3 cccccc

习题 21: 函数可以返回东西

[root@localhost py]#cat func-return.py#!/usr/bin/env python#-*- coding:utf-8 -*-

defadd(a, b):print "ADDING %d + %d" %(a, b)return a +bdefsubtract(a, b):print "SUBTRACTING %d - %d" %(a, b)return a -bdefmultiply(a, b):print "MULTIPLYING %d * %d" %(a, b)return a *bdefdivide(a, b):print "DIVIDING %d / %d" %(a, b)return a /bprint "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.# pullzle:智力题

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?"

[root@localhost py]#python func-return.py

Let's do some math with just functions!

ADDING 30 + 5SUBTRACTING78 - 4MULTIPLYING90 * 2DIVIDING100 / 2Age:35, Height: 74, Weight: 180, IQ: 50Hereisa puzzle.

DIVIDING50 / 2MULTIPLYING180 * 25SUBTRACTING74 - 4500ADDING35 + -4426That becomes:-4391 Can you do it by hand?

习题 24: 练习

[root@localhost py]#cat practise.py#!/usr/bin/env python

print "Let's practice everything."

print 'You\'d need to know \'bout escapes with \\ that do \nnewlines 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 "--------------"

printpoemprint "--------------"five= 10 - 2 + 3 - 6

print "This should be five: %s" %fivedefsecret_formula(started):

jelly_beans= started * 500jars= jelly_beans / 1000crates= jars / 100

returnjelly_beans, jars, crates

start_point= 10000beans, jars, crates=secret_formula(start_point)print "With a starting point of: %d" %start_pointprint "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_formula(start_point)

[root@localhost py]#python practise.py

Let's practice everything.

You'd need to know'bout escapes with \ that do

newlinesandtabs.--------------The lovely world

with logic so firmly planted

cannot discern

the needs of love

nor comprehend passionfromintuitionandrequires an explanation

where thereisnone.--------------This should be five:5With a starting point of:10000We'd have 5000000 beans, 5000 jars, and 50 crates.

We can also do that this way:

We'd have 500000 beans, 500 jars, and 5 crates.

习题 25: 更多的练习

[root@localhost py]#cat practise2.py#!/usr/bin/env python

defbreak_words(stuff):"""This function will break up words for us."""words= stuff.split('')returnwordsdefsort_words(words):"""Sorts the words."""

returnsorted(words)defprint_first_word(words):"""Prints the first word after popping it off."""word=words.pop(0)printworddefprint_last_word(words):"""Prints the last word after popping it off."""word= words.pop(-1)printworddefsort_sentence(sentence):"""Takes in a full sentence and returns the sorted words."""words=break_words(sentence)returnsort_words(words)defprint_first_and_last(sentence):"""Prints the first and last words of the sentence."""words=break_words(sentence)

print_first_word(words)

print_last_word(words)defprint_first_and_last_sorted(sentence):"""Sorts the words then prints the first and last one."""words=sort_sentence(sentence)

print_first_word(words)

print_last_word(words)

习题26：逻辑术语

在 python 中我们会用到下面的术语(字符或者词汇)来定义事物的真(True)或者假(False)。计算机的逻辑就是在程序的某个位置检查这些字符或者变量组合

在一起表达的结果是真是假。

 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

我们将使用这些字符来创建你需要记住的真值表。

not False True

not True False

True or FalseTrue

True or True True

False or True True

False or False False

True and FalseFalse

True and True True

False and True False

False and False False

not (True or False) False

not (True or True) False

not (False or True) False

not (False or False) True

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27：bool 值运算

[root@localhost py]# cat bool.py

#!/usr/bin/env python

print True and True

print False and True

print 1 == 1 and 2 == 1

print "test" == "test"

print 1 == 1 or 2 != 1

print True and 1 == 1

print False and 0 != 0

print True or 1 == 1

print "test" == "testing"

print 1 != 0 and 2 == 1

print "test" != "testing"

print "test" == 1

print not (True and False)

print not (1 == 1 and 0 != 1)

print not (10 == 1 or 1000 == 1000)

print not (1 != 10 or 3 == 4)

print not ("testing" == "testing" and "Zed" == "Cool Guy")

print 1 == 1 and not ("testing" == 1 or 1 == 0)

print "chunky" == "bacon" and not (3 == 4 or 3 == 3)

print 3 == 3 and not ("testing" == "testing" or "Python" == "Fun")

[root@localhost py]# python bool.py

True

False

False

True

True

True

False

True

False

False

True

False

True

False

False

False

True

True

False

False

习题28：bool运算

3 != 4 and not ("testing" != "test" or "Python" == "Python")

接下来你将看到这个复杂表达式是如何逐级解为一个单独结果的：1. 解出每一个等值判断:

a.3 != 4 为 True : True and not ("testing" != "test" or "P

ython"=="Python")

b. "testing" != "test" 为 True : True and not (True or "Pyt

hon"=="Python")

c. "Python" == "Python" : True and not (True orTrue)2. 找到括号中的每一个 and/or:

a. (Trueor True) 为 True: True and not(True)3. 找到每一个 not并将其逆转:

a.not (True) 为 False: True andFalse4. 找到剩下的 and/or，解出它们的值:

a. TrueandFalse 为 False

这样我们就解出了它最终的值为 False.

View Code

习题 29: 如果(if)

[root@localhost py]#cat if.py#!/usr/bin/env python

people = 20cats= 30dogs= 15

if people

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

if people

if people >dogs:print "The world is 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."

View Code

[root@localhost py]#python if.py

Too many cats! The world isdoomed!

The worldisdry!

People are greater thanorequal to dogs.

People are less thanorequal to dogs.

People are dogs.

View Code

习题30：if -elase 结合使用

[root@localhost py]#cat if.py#!/usr/bin/env python

people = 20cats= 30dogs= 15

if people

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

if people

if people >dogs:print "The world is 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."

View Code

[root@localhost py]# python if-else.py

We should take the cars.

Maybe we could take the buses.

Alright, let's just take the buses.