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 python from sys import argv from os.path import exists script,from_file,to_file = argv print "Copying from %s to %s" %(from_file,to_file) # we could do 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 from cc.txt to dd.txt The input file is 11 bytes long Does the output file exist? True Ready,hit RETURN to continue, 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 = args print "arg1:%r,arg2:%r" %(arg1,arg2) # ok,that *args is actually pointless,we can just do this def print_two_again(arg1,arg2): print "arg1:%r,arg2:%r" %(arg1,arg2) # this just takes one argument def print_one(arg1): print "arg1:%r"% arg1 # this one takes no arguments def print_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 def cheese_and_crackers(cheese_count, boxes_of_crackers): print "You have %d cheeses!" % cheese_count print "You have %d boxes of crackers!" % boxes_of_crackers print "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 = 10 amount_of_crackers = 50 cheese_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 have 20 cheeses! You have 30 boxes of crackers! Man that's enough for a party! Get a blanket. OR, we can use variables from our script: You have 10 cheeses! You have 50 boxes of crackers! Man that's enough for a party! Get a blanket. We can even do math inside too: You have 30 cheeses! You have 11 boxes of crackers! Man that's enough for a party! Get a blanket. And we can combine the two, variables and math: You have 110 cheeses! You have 1050 boxes 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 import argv script, input_file = argv def print_all(f): print f.read() def rewind(f): f.seek(0) def print_a_line(line_count, f): print line_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 = 1 print_a_line(current_line, current_file) current_line = current_line + 1 print_a_line(current_line, current_file) current_line = current_line + 1 print_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: 1 aaaaaa 2 bbbbbb 3 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 -*- 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.# 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 + 5 SUBTRACTING 78 - 4 MULTIPLYING 90 * 2 DIVIDING 100 / 2 Age: 35, Height: 74, Weight: 180, IQ: 50 Here is a puzzle. DIVIDING 50 / 2 MULTIPLYING 180 * 25 SUBTRACTING 74 - 4500 ADDING 35 + -4426 That 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 "--------------" print poem print "--------------" five = 10 - 2 + 3 - 6 print "This should be five: %s" % five def secret_formula(started): jelly_beans = started * 500 jars = jelly_beans / 1000 crates = jars / 100 return jelly_beans, jars, crates start_point = 10000 beans, jars, crates = secret_formula(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_formula(start_point)
[root@localhost py]# python practise.py Let's practice everything. You'd need to know 'bout escapes with \ that do newlines and tabs. -------------- The lovely world with logic so firmly planted cannot discern the needs of love nor comprehend passion from intuition and requires an explanation where there is none. -------------- This should be five: 5 With a starting point of: 10000 We'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 def break_words(stuff): """This function will break up words for us.""" words = stuff.split('') return words def sort_words(words): """Sorts the words.""" return sorted(words) def print_first_word(words): """Prints the first word after popping it off.""" word = words.pop(0) print word def print_last_word(words): """Prints the last word after popping it off.""" word = words.pop(-1) print word def sort_sentence(sentence): """Takes in a full sentence and returns the sorted words.""" words = break_words(sentence) return sort_words(words) def print_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) def print_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 False True
True or True True
False or True True
False or False False
True and False False
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 or True) 2. 找到括号中的每一个 and/or : a. (True or 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 and False 4. 找到剩下的 and/or，解出它们的值: a. True and False 为 False 这样我们就解出了它最终的值为 False.
习题 29: 如果(if)
[root@localhost py]# cat if.py #!/usr/bin/env python 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 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."
[root@localhost py]# python if.py Too many cats! The world is doomed! The world is dry! People are greater than or equal to dogs. People are less than or equal to dogs. People are dogs.
习题30：if -elase 结合使用
[root@localhost py]# cat if.py #!/usr/bin/env python 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 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."
[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.