Python基础实例
1 你好
#打开新窗口,输入:
#! /usr/bin/python
# -*- coding: utf8 -*-
s1=input("Input your name:")
print("你好,%s" % s1)
'''
知识点:
* input("某字符串")函数:显示"某字符串",并等待用户输入.
* print()函数:如何打印.
* 如何应用中文
* 如何用多行注释
'''
2 字符串和数字
但有趣的是,在javascript里我们会理想当然的将字符串和数字连接,因为是动态语言嘛.但在Python里有点诡异,如下:
#! /usr/bin/python
a=2
b="test"
c=a+b
运行这行程序会出错,提示你字符串和数字不能连接,于是只好用内置函数进行转换
#! /usr/bin/python
#运行这行程序会出错,提示你字符串和数字不能连接,于是只好用内置函数进行转换
a=2
b="test"
c=str(a)+b
d="1111"
e=a+int(d)
#How to print multiply values
print ("c is %s,e is %i" % (c,e))
'''
知识点:
* 用int和str函数将字符串和数字进行转换
* 打印以#开头,而不是习惯的//
* 打印多个参数的方式
'''
3 列表
#! /usr/bin/python
# -*- coding: utf8 -*-
#列表类似Javascript的数组,方便易用
#定义元组
word=['a','b','c','d','e','f','g']
#如何通过索引访问元组里的元素
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.
#元组可以合并
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)
#删除元素
del word[0]
print (word)
del word[1:3]
print (word)
'''
知识点:
* 列表长度是动态的,可任意添加删除元素.
* 用索引可以很方便访问元素,甚至返回一个子列表
* 更多方法请参考Python的文档
'''
4 字典
#! /usr/bin/python
x={'a':'aaa','b':'bbb','c':12}
print (x['a'])
print (x['b'])
print (x['c'])
for key in x:
print ("Key is %s and value is %s" % (key,x[key]))
'''
知识点:
* 将他当Java的Map来用即可.
'''
5 字符串
比起C/C++,Python处理字符串的方式实在太让人感动了.把字符串当列表来用吧.
#! /usr/bin/python
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))
中文和英文的字符串长度是否一样?
#! /usr/bin/python
# -*- coding: utf8 -*-
s=input("输入你的中文名,按回车继续");
print ("你的名字是 : " +s)
l=len(s)
print ("你中文名字的长度是:"+str(l))
知识点:
- 类似Java,在python3里所有字符串都是unicode,所以长度一致.
6 条件和循环语句
#! /usr/bin/python
#条件和循环语句
x=int(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))
#知识点:
# * 条件和循环语句
# * 如何得到控制台输入
7 函数
#! /usr/bin/python
# -*- coding: utf8 -*-
def sum(a,b):
return a+b
func = sum
r = func(5,6)
print (r)
# 提供默认值
def add(a,b=2):
return a+b
r=add(1)
print (r)
r=add(1,5)
print (r)
一个好用的函数
#! /usr/bin/python
# -*- coding: utf8 -*-
# The range() function
a =range (1,10)
for i in a:
print (i)
a = range(-2,-11,-3) # The 3rd parameter stands for step
for i in a:
print (i)
知识点:
- Python 不用{}来控制程序结构,他强迫你用缩进来写程序,使代码清晰.
- 定义函数方便简单
- 方便好用的range函数
8 异常处理
#! /usr/bin/python
s=input("Input your age:")
if s =="":
raise Exception("Input must no be empty.")
try:
i=int(s)
except Exception as err:
print(err)
finally: # Clean up action
print("Goodbye!")
9 文件处理
对比Java,python的文本处理再次让人感动
#! /usr/bin/python
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("每一行的数据是:%s"%line)
f.close()
知识点:
- open的参数:r表示读,w写数据,在写之前先清空文件内容,a打开并附加内容.
- 打开文件之后记得关闭
10 类和继承
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))
'''
知识点:
* self:类似Java的this参数
'''
11 包机制
每一个.py文件称为一个module,module之间可以互相导入.请参看以下例子:
# a.py
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"
module可以定义在包里面.Python定义包的方式稍微有点古怪,假设我们有一个parent文件夹,该文件夹有一个child子文件夹.child中有一个module a.py . 如何让Python知道这个文件层次结构?很简单,每个目录都放一个名为_init_.py 的文件.该文件内容可以为空.这个层次结构如下所示:
parent
--__init_.py
--child
-- __init_.py
--a.py
b.py
那么Python如何找到我们定义的module?在标准包sys中,path属性记录了Python的包路径.你可以将之打印出来:
import sys
print(sys.path)
通常我们可以将module的包路径放到环境变量PYTHONPATH中,该环境变量会自动添加到sys.path属性.另一种方便的方法是编程中直接指定我们的module路径到sys.path 中:
import sys
import os
sys.path.append(os.getcwd()+'\\parent\\child')
print(sys.path)
from 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))
知识点:
- 如何定义模块和包
- 如何将模块路径添加到系统路径,以便python找到它们
- 如何得到当前路径
12 内建帮助手册
对比C++,Java的突出进步是内建Javadoc机制,程序员可以通过阅读Javadoc了解函数用法.Python也内建了一些方便函数以便程序员参考.
- dir函数: 查看某个类/对象的方法. 如果有某个方法想不起来,请敲dir. 在idle里,试试 dir(list)
- help函数: 详细的类/对象介绍. 在idle里, 试试 help(list)
1 遍历文件夹和文件
import os
import os.path
# os,os.path里包含大多数文件访问的函数,所以要先引入它们.
# 请按照你的实际情况修改这个路径
rootdir = " d:/download "
for parent, dirnames, filenames in os.walk(rootdir):
# case 1:
for dirname in dirnames:
print ( " parent is: " + parent)
print ( " dirname is: " + dirname)
# case 2
for filename in filenames:
print ( " parent is: " + parent)
print ( " filename with full path : " + os.path.join(parent, filename))
''' 知识点:
* os.walk返回一个三元组.其中dirnames是所有文件夹名字(不包含路径),filenames是所有文件的名字(不包含路径).parent表示父目录.
* case1 演示了如何遍历所有目录.
* case2 演示了如何遍历所有文件.
* os.path.join(dirname,filename) : 将形如"/a/b/c"和"d.java"变成/a/b/c/d.java".
'''
2 分割路径和文件名
import os.path
# 常用函数有三种:分隔路径,找出文件名.找出盘符(windows系统),找出文件的扩展名.
# 根据你机器的实际情况修改下面参数.
spath = " D:/download/repository.7z "
# case 1:
p,f = os.path.split(spath);
print ( " dir is: " + p)
print ( " file is: " + f)
# case 2:
drv,left = os.path.splitdrive(spath);
print ( " driver is: " + drv)
print ( " left is: " + left)
# case 3:
f,ext = os.path.splitext(spath);
print ( " f is: " + f)
print ( " ext is: " + ext)
'''
知识点: 这三个函数都返回二元组.
* case1 分隔目录和文件名
* case2 分隔盘符和文件名
* case3 分隔文件和扩展名
'''
总结:5个函数
- os.walk(spath)
- os.path.split(spath)
- os.path.splitdrive(spath)
- os.path.splitext(spath)
- os.path.join(path1,path2)
3 复制文件
import shutil
import os
import os.path
src = " d:\\download\\test\\myfile1.txt "
dst = " d:\\download\\test\\myfile2.txt "
dst2 = " d:/download/test/测试文件夹.txt "
dir1 = os.path.dirname(src)
print ( " dir1 %s " % dir1)
if (os.path.exists(src) == False):
os.makedirs(dir1)
f1 = open(src, " w " )
f1.write( " line a\n " )
f1.write( " line b\n " )
f1.close()
shutil.copyfile(src, dst)
shutil.copyfile(src, dst2)
f2 = open(dst, " r " )
for line in f2:
print (line)
f2.close()
# 测试复制文件夹树
try :
srcDir = " d:/download/test "
dstDir = " d:/download/test2 "
# 如果dstDir已经存在,那么shutil.copytree方法会报错!
# 这也意味着你不能直接用d:作为目标路径.
shutil.copytree(srcDir, dstDir)
except Exception as err:
print (err)
'''
知识点:
* shutil.copyfile:如何复制文件
* os.path.exists:如何判断文件夹是否存在
* shutil.copytree:如何复制目录树
'''
总结:4个函数
- os.path.dirname(path)
- os.path.exists(path)
- shutil.copyfile(src, dst)
- shutil.copytree(srcDir, dstDir)
4 实战:文件备份小程序
import os
import shutil
import datetime
'''
作用：将目录备份到其他路径。
实际效果：
假设给定目录"/media/data/programmer/project/python" ，
备份路径"/home/diegoyun/backup/“ ，
则会将python目录备份到备份路径下，形如：
/home/diegoyun/backup/yyyymmddHHMMSS/python/xxx/yyy/zzz..
用法:更改这两个参数.
backdir:备份目的地.
copydirs:想要备份的文件夹.
'''
def mainLogic():
# add dirs you want to copy
backdir = " d:\\test "
print (backdir)
copydirs = []
copydirs.append( " d:\\temp " );
# copydirs.append("d:\\test");
print ( " Copying files =================== " )
start = datetime.datetime.now()
# gen a data folder for backup
backdir = os.path.join(backdir,start.strftime( " %Y-%m-%d " ))
# print("backdir is:"+backdir)
kc = 0
for d in copydirs:
kc = kc + copyFiles(d,backdir)
end = datetime.datetime.now()
print ( " Finished! =================== " )
print ( " Total files : " + str(kc) )
print ( " Elapsed time : " + str((end - start).seconds) + " seconds " )
def copyFiles(copydir,backdir):
prefix = getPathPrefix(copydir)
# print("prefix is:"+prefix )
i = 0
for dirpath,dirnames,filenames in os.walk(copydir):
for name in filenames:
oldpath = os.path.join(dirpath,name)
newpath = omitPrefix(dirpath,prefix)
print ( " backdir is: " + backdir )
newpath = os.path.join(backdir,newpath)
print ( " newpath is: " + newpath)
if os.path.exists(newpath) != True:
os.makedirs(newpath)
newpath = os.path.join(newpath,name)
print ( " From: " + oldpath + " to: " + newpath)
shutil.copyfile(oldpath,newpath)
i = i + 1
return i
def getPathPrefix(fullpath):
# Giving /media/data/programmer/project/ , get the prefix
# /media/data/programmer/
l = fullpath.split(os.path.sep)
# print(str(l[-1]=="")
if l[ - 1 ] == "" :
tmp = l[ - 2 ]
else :
tmp = l[ - 1 ]
return fullpath[0:len(fullpath) - len(tmp) - 1 ]
def omitPrefix(fullpath,prefix):
# Giving /media/data/programmer/project/python/tutotial/file/test.py ,
# and prefix is Giving /media/data/programmer/project/,
# return path as python/tutotial/file/test.py
return fullpath[len(prefix) + 1 :]
mainLogic()
5 资源:方法详解
你可以在这里看到更多的api解释,感谢该作者: http://www.cnpython.org/docs/200/p_119.html
