Python 超詳細(xì)的入門教程
2018-07-20 來源：編程學(xué)習(xí)網(wǎng)
為什么使用Python
假設(shè)我們有這么一項(xiàng)任務(wù):簡單測試局域網(wǎng)中的電腦是否連通.這些電腦的ip范圍從192.168.0.101到192.168.0.200.思路:用shell編程.(Linux通常是bash而Windows是批處理腳本).例如,在Windows上用ping ip 的命令依次測試各個(gè)機(jī)器并得到控制臺(tái)輸出.由于ping通的時(shí)候控制臺(tái)文本通常是"Reply from ... " 而不通的時(shí)候文本是"time out ... " ,所以,在結(jié)果中進(jìn)行字符串查找,即可知道該機(jī)器是否連通.
實(shí)現(xiàn):Java代碼如下:
String cmd="cmd.exe ping ";
String ipprefix="192.168.10.";
int begin=101;
int end=200;
Process p=null;
for(int i=begin;i<end;i++){
p= Runtime.getRuntime().exec(cmd+i);
String line = null;
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
while((line = reader.readLine()) != null)
{
//Handling line , may logs it.
}
reader.close();
p.destroy();
}
String ipprefix="192.168.10.";
int begin=101;
int end=200;
Process p=null;
for(int i=begin;i<end;i++){
p= Runtime.getRuntime().exec(cmd+i);
String line = null;
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
while((line = reader.readLine()) != null)
{
//Handling line , may logs it.
}
reader.close();
p.destroy();
}
這段代碼運(yùn)行得很好,問題是為了運(yùn)行這段代碼,你還需要做一些額外的工作.這些額外的工作包括:
- 編寫一個(gè)類文件
- 編寫一個(gè)main方法
- 將之編譯成字節(jié)代碼
- 由于字節(jié)代碼不能直接運(yùn)行,你需要再寫個(gè)小小的bat或者bash腳本來運(yùn)行.
同樣的工作用Python實(shí)現(xiàn)如下:
import subprocess
cmd="cmd.exe"
begin=101
end=200
while begin<end:
p=subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,
stdin=subprocess.PIPE,
stderr=subprocess.PIPE)
p.stdin.write("ping 192.168.1."+str(begin)+"\n")
p.stdin.close()
p.wait()
print "execution result: %s"%p.stdout.read()
對比Java,Python的實(shí)現(xiàn)更為簡潔,你編寫的時(shí)間更快.你不需要寫main函數(shù),并且這個(gè)程序保存之后可以直接運(yùn)行.另外,和Java一樣,Python也是跨平臺(tái)的.
有經(jīng)驗(yàn)的C/Java程序員可能會(huì)爭論說用C/Java寫會(huì)比Python寫得快.這個(gè)觀點(diǎn)見仁見智.我的想法是當(dāng)你同時(shí)掌握J(rèn)ava和Python之后,你會(huì)發(fā)現(xiàn)用Python寫這類程序的速度會(huì)比Java快上許多.例如操作本地文件時(shí)你僅需要一行代碼而不需要Java的許多流包裝類.各種語言有其天然的適合的應(yīng)用范圍.用Python處理一些簡短程序類似與操作系統(tǒng)的交互編程工作最省時(shí)省力.
Python應(yīng)用場合
足夠簡單的任務(wù),例如一些shell編程.如果你喜歡用Python設(shè)計(jì)大型商業(yè)網(wǎng)站或者設(shè)計(jì)復(fù)雜的游戲,悉聽尊便.2 快速入門
2.1 Hello world
安裝完P(guān)ython之后(我本機(jī)的版本是2.5.4),打開IDLE(Python GUI) , 該程序是Python語言解釋器,你寫的語句能夠立即運(yùn)行.我們寫下一句著名的程序語句:
print "Hello,world!"
并按回車.你就能看到這句被K&R引入到程序世界的名言.
在解釋器中選擇"File"--"New Window" 或快捷鍵 Ctrl+N , 打開一個(gè)新的編輯器.寫下如下語句:
print "Hello,world!"
raw_input("Press enter key to close this window
");
raw_input("Press enter key to close this window
");
保存為a.py文件.按F5,你就可以看到程序的運(yùn)行結(jié)果了.這是Python的第二種運(yùn)行方式.
找到你保存的a.py文件,雙擊.也可以看到程序結(jié)果.Python的程序能夠直接運(yùn)行,對比Java,這是一個(gè)優(yōu)勢.
2.2 國際化支持
我們換一種方式來問候世界.新建一個(gè)編輯器并寫如下代碼:
print "歡迎來到奧運(yùn)中國!"
raw_input("Press enter key to close this window");
raw_input("Press enter key to close this window
");
在你保存代碼的時(shí)候,Python會(huì)提示你是否改變文件的字符集,結(jié)果如下:
# -*- coding: cp936 -*-
print "歡迎來到奧運(yùn)中國!"
raw_input("Press enter key to close this window");
print "歡迎來到奧運(yùn)中國!"
raw_input("Press enter key to close this window
");
將該字符集改為我們更熟悉的形式:
# -*- coding: GBK -*-
print "歡迎來到奧運(yùn)中國!" # 使用中文的例子
raw_input("Press enter key to close this window");
print "歡迎來到奧運(yùn)中國!" # 使用中文的例子
raw_input("Press enter key to close this window
");
程序一樣運(yùn)行良好.
2.3 方便易用的計(jì)算器
用微軟附帶的計(jì)算器來計(jì)數(shù)實(shí)在太麻煩了.打開Python解釋器,直接進(jìn)行計(jì)算:
a=100.0
b=201.1
c=2343
print (a+b+c)/c
b=201.1
c=2343
print (a+b+c)/c
2.4 字符串,ASCII和UNICODE
可以如下打印出預(yù)定義輸出格式的字符串:
print """
Usage: thingy [OPTIONS]
-h Display this usage message
-H hostname Hostname to connect to
"""
Usage: thingy [OPTIONS]
-h Display this usage message
-H hostname Hostname to connect to
"""
字符串是怎么訪問的?請看這個(gè)例子:
word="abcdefg"
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "+b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "+c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "+d # All elements of word.
e=word[:2]+word[2:]
print "e is: "+e # All elements of word.
f=word[-1]
print "f is: "+f # The last elements of word.
g=word[-4:-2]
print "g is: "+g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "+h # The last two elements.
i=word[:-2]
print "i is: "+i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "+b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "+c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "+d # All elements of word.
e=word[:2]+word[2:]
print "e is: "+e # All elements of word.
f=word[-1]
print "f is: "+f # The last elements of word.
g=word[-4:-2]
print "g is: "+g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "+h # The last two elements.
i=word[:-2]
print "i is: "+i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
請注意ASCII和UNICODE字符串的區(qū)別:
print "Input your Chinese name:"
s=raw_input("Press enter to be continued");
print "Your name is : " +s;
l=len(s)
print "Length of your Chinese name in asc codes is:"+str(l);
a=unicode(s,"GBK")
l=len(a)
print "I'm sorry we should use unicode char!Characters number of your Chinese \
name in unicode is:"+str(l);
s=raw_input("Press enter to be continued
");print "Your name is
: " +s;l=len(s)
print "Length of your Chinese name in asc codes is:"+str(l);
a=unicode(s,"GBK")
l=len(a)
print "I'm sorry we should use unicode char!Characters number of your Chinese \
name in unicode is:"+str(l);
2.5 使用List
類似Java里的List,這是一種方便易用的數(shù)據(jù)類型:
word=['a','b','c','d','e','f','g']
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "
print b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "
print c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "
print d # All elements of word.
e=word[:2]+word[2:]
print "e is: "
print e # All elements of word.
f=word[-1]
print "f is: "
print f # The last elements of word.
g=word[-4:-2]
print "g is: "
print g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "
print h # The last two elements.
i=word[:-2]
print "i is: "
print i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
print "Adds new element"
word.append('h')
print word
a=word[2]
print "a is: "+a
b=word[1:3]
print "b is: "
print b # index 1 and 2 elements of word.
c=word[:2]
print "c is: "
print c # index 0 and 1 elements of word.
d=word[0:]
print "d is: "
print d # All elements of word.
e=word[:2]+word[2:]
print "e is: "
print e # All elements of word.
f=word[-1]
print "f is: "
print f # The last elements of word.
g=word[-4:-2]
print "g is: "
print g # index 3 and 4 elements of word.
h=word[-2:]
print "h is: "
print h # The last two elements.
i=word[:-2]
print "i is: "
print i # Everything except the last two characters
l=len(word)
print "Length of word is: "+ str(l)
print "Adds new element
"word.append('h')
print word
2.6 條件和循環(huán)語句
# Multi-way decision
x=int(raw_input("Please enter an integer:"))
if x<0:
x=0
print "Negative changed to zero"
elif x==0:
print "Zero"
else:
print "More"
# Loops List
a = ['cat', 'window', 'defenestrate']
for x in a:
print x, len(x)
x=int(raw_input("Please enter an integer:"))
if x<0:
x=0
print "Negative changed to zero"
elif x==0:
print "Zero"
else:
print "More"
# Loops List
a = ['cat', 'window', 'defenestrate']
for x in a:
print x, len(x)
2.7 如何定義函數(shù)
# Define and invoke function.
def sum(a,b):
return a+b
func = sum
r = func(5,6)
print r
# Defines function with default argument
def add(a,b=2):
return a+b
r=add(1)
print r
r=add(1,5)
print r
def sum(a,b):
return a+b
func = sum
r = func(5,6)
print r
# Defines function with default argument
def add(a,b=2):
return a+b
r=add(1)
print r
r=add(1,5)
print r
并且,介紹一個(gè)方便好用的函數(shù):
# The range() function
a =range(5,10)
print a
a = range(-2,-7)
print a
a = range(-7,-2)
print a
a = range(-2,-11,-3) # The 3rd parameter stands for step
print a
a =range(5,10)
print a
a = range(-2,-7)
print a
a = range(-7,-2)
print a
a = range(-2,-11,-3) # The 3rd parameter stands for step
print a
2.8 文件I/O
spath="D:/download/baa.txt"
f=open(spath,"w") # Opens file for writing.Creates this file doesn't exist.
f.write("First line 1.\n")
f.writelines("First line 2.")
f.close()
f=open(spath,"r") # Opens file for reading
for line in f:
print line
f.close()
f=open(spath,"w") # Opens file for writing.Creates this file doesn't exist.
f.write("First line 1.\n")
f.writelines("First line 2.")
f.close()
f=open(spath,"r") # Opens file for reading
for line in f:
print line
f.close()
2.9 異常處理
s=raw_input("Input your age:")
if s =="":
raise Exception("Input must no be empty.")
try:
i=int(s)
except ValueError:
print "Could not convert data to an integer."
except:
print "Unknown exception!"
else: # It is useful for code that must be executed if the try clause does not raise an exception
print "You are %d" % i," years old"
finally: # Clean up action
print "Goodbye!"
if s =="":
raise Exception("Input must no be empty.")
try:
i=int(s)
except ValueError:
print "Could not convert data to an integer."
except:
print "Unknown exception!"
else: # It is useful for code that must be executed if the try clause does not raise an exception
print "You are %d" % i," years old"
finally: # Clean up action
print "Goodbye!"
2.10 類和繼承
class Base:
def __init__(self):
self.data = []
def add(self, x):
self.data.append(x)
def addtwice(self, x):
self.add(x)
self.add(x)
# Child extends Base
class Child(Base):
def plus(self,a,b):
return a+b
oChild =Child()
oChild.add("str1")
print oChild.data
print oChild.plus(2,3)
def __init__(self):
self.data = []
def add(self, x):
self.data.append(x)
def addtwice(self, x):
self.add(x)
self.add(x)
# Child extends Base
class Child(Base):
def plus(self,a,b):
return a+b
oChild =Child()
oChild.add("str1")
print oChild.data
print oChild.plus(2,3)
2.11 包機(jī)制
每一個(gè).py文件稱為一個(gè)module,module之間可以互相導(dǎo)入.請參看以下例子:
# a.py
def add_func(a,b):
return a+b
def add_func(a,b):
return a+b
# b.py
from a import add_func # Also can be : import a
print "Import add_func from module a"
print "Result of 1 plus 2 is: "
print add_func(1,2) # If using "import a" , then here should be "a.add_func"
from a import add_func # Also can be : import a
print "Import add_func from module a"
print "Result of 1 plus 2 is: "
print add_func(1,2) # If using "import a" , then here should be "a.add_func"
module可以定義在包里面.Python定義包的方式稍微有點(diǎn)古怪,假設(shè)我們有一個(gè)parent文件夾,該文件夾有一個(gè)child子文件夾.child中有一個(gè)module a.py . 如何讓Python知道這個(gè)文件層次結(jié)構(gòu)?很簡單,每個(gè)目錄都放一個(gè)名為_init_.py 的文件.該文件內(nèi)容可以為空.這個(gè)層次結(jié)構(gòu)如下所示:
parent
--__init_.py
--child
-- __init_.py
--a.py
b.py
--__init_.py
--child
-- __init_.py
--a.py
b.py
那么Python如何找到我們定義的module?在標(biāo)準(zhǔn)包sys中,path屬性記錄了Python的包路徑.你可以將之打印出來:
import sys
print sys.path
print sys.path
通常我們可以將module的包路徑放到環(huán)境變量PYTHONPATH中,該環(huán)境變量會(huì)自動(dòng)添加到sys.path屬性.另一種方便的方法是編程中直接指定我們的module路徑到sys.path 中:
import sys
sys.path.append('D:\\download')
from parent.child.a import add_func
print sys.path
print "Import add_func from module a"
print "Result of 1 plus 2 is: "
print add_func(1,2)
sys.path.append('D:\\download')
from parent.child.a import add_func
print sys.path
print "Import add_func from module a"
print "Result of 1 plus 2 is: "
print add_func(1,2)
總結(jié)
你會(huì)發(fā)現(xiàn)這個(gè)教程相當(dāng)?shù)暮唵?許多Python特性在代碼中以隱含方式提出,這些特性包括:Python不需要顯式聲明數(shù)據(jù)類型,關(guān)鍵字說明,字符串函數(shù)的解釋等等.我認(rèn)為一個(gè)熟練的程序員應(yīng)該對這些概念相當(dāng)了解,這樣在你擠出寶貴的一小時(shí)閱讀這篇短短的教程之后,你能夠通過已有知識(shí)的遷移類比盡快熟悉Python,然后盡快能用它開始編程.當(dāng)然,1小時(shí)學(xué)會(huì)Python頗有嘩眾取寵之嫌.確切的說,編程語言包括語法和標(biāo)準(zhǔn)庫.語法相當(dāng)于武術(shù)招式,而標(biāo)準(zhǔn)庫應(yīng)用實(shí)踐經(jīng)驗(yàn)則類似于內(nèi)功,需要長期鍛煉.Python學(xué)習(xí)了Java的長處,提供了大量極方便易用的標(biāo)準(zhǔn)庫供程序員"拿來主義".(這也是Python成功的原因),在開篇我們看到了Python如何調(diào)用Windows cmd的例子,以后我會(huì)盡量寫上各標(biāo)準(zhǔn)庫的用法和一些應(yīng)用技巧,讓大家真正掌握Python.
標(biāo)簽： isp linux 代碼 腳本 數(shù)據(jù)庫 網(wǎng)絡(luò)
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