python集合例题_python练习题集合-2
author：headsen chen
date：2018-06-01?15:39:26
習題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.
檢驗新生成的dd.txt文件：
[root@localhost py]# cat dd.txt
1234567890
這里不過dd.txt是否存在，若存在：清空然后復制cc.txt的內容過來，若不存在dd.txt文件就創建dd.txt文件并復制內容過來
補充：exists這個命令將文件名字符串作為參數，如果文件存在的話，它將返回 True，否則將返回 False。
習題18：函數 ---> 理解成“迷你腳本”
函數可以做三樣事情：
1.它們給代碼片段命名，就跟“變量”給字符串和數字命名一樣。
2.它們可以接受參數，就跟你的腳本接受 argv 一樣。
3.通過使用 #1 和 #2，它們可以讓你創建“微型腳本”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.
習題 19: 函數和變量
[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.
習題 20: 函數和文件
[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
習題 21: 函數可以返回東西
[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:智力題
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?
習題 24: 練習
[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.
習題 25: 更多的練習
[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)
習題26：邏輯術語
在 python 中我們會用到下面的術語(字符或者詞匯)來定義事物的真(True)或者假(False)。計算機的邏輯就是在程序的某個位置檢查這些字符或者變量組合
在一起表達的結果是真是假。
? and 與
? 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
我們將使用這些字符來創建你需要記住的真值表。
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
習題27：bool 值運算
[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
習題28：bool運算
3 != 4 and not ("testing" != "test" or "Python" == "Python")
接下來你將看到這個復雜表達式是如何逐級解為一個單獨結果的：1. 解出每一個等值判斷:
a.3 != 4 為 True : True and not ("testing" != "test" or "P
ython"=="Python")
b. "testing" != "test" 為 True : True and not (True or "Pyt
hon"=="Python")
c. "Python" == "Python" : True and not (True orTrue)2. 找到括號中的每一個 and/or:
a. (Trueor True) 為 True: True and not(True)3. 找到每一個 not并將其逆轉:
a.not (True) 為 False: True andFalse4. 找到剩下的 and/or，解出它們的值:
a. TrueandFalse 為 False
這樣我們就解出了它最終的值為 False.
View Code
習題 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
習題30：if -elase 結合使用
[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.
總結
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