Python學習筆記

目錄

1、安裝、編譯與運行

2、變量、運算與表達式

3、數據類型

      一、數字

      二、字符串

      三、元組

      四、列表

      五、字典

4、流程控制

      一、if-else

      二、for

      三、while

      四、switch

5、函數

      一、自定義函數

      二、Lambda函數

      三、Python內置函數

6、包與模塊

      一、模塊module

      二、包package

7、正則表達式

      一、元字符

      二、經常使用函數

      三、分組 

      四、一個小實例-爬蟲

8、深拷貝與淺拷貝

9、文件與目錄

      一、文件讀寫

      二、OS模塊

      三、目錄遍歷

10、異常處理

 

1、安裝、編譯與運行

       Python的安裝很容易，直接到官網：http://www.python.org/下載安裝就能夠了。Ubuntu通常都預安裝了。沒有的話，就能夠#apt-get install python。Windows的話直接下載msi包安裝便可。Python 程序是經過解釋器執行的，因此安裝後，能夠看到Python提供了兩個解析器，一個是IDLE (Python GUI)，一個是Python (command line)。前者是一個帶GUI界面的版本，後者實際上和在命令提示符下運行python是同樣的。運行解釋器後，就會有一個命令提示符>>>，在提示符後鍵入你的程序語句，鍵入的語句將會當即執行。就像Matlab同樣。

       另外，Matlab有.m的腳步文件，python也有.py後綴的腳本文件，這個文件除了能夠解釋執行外，還能夠編譯運行，編譯後運行速度要比解釋運行要快。

       例如，我要打印一個helloWorld。

方法1：直接在解釋器中，>>> print ‘helloWorld’。

方法2：將這句代碼寫到一個文件中，例如hello.py。運行這個文件有三種方式：

1）在終端中：python hello.py

2）先編譯成.pyc文件：

import py_compile

py_compile.compile("hello.py")

再在終端中：python hello.pyc

3）在終端中：

python -O -m py_compile hello.py

python hello.pyo

       編譯成.pyc和.pyo文件後，執行的速度會更快。因此通常一些重複性並屢次調用的代碼會被編譯成這兩種可執行的方式來待調用。

 

2、變量、運算與表達式

         這裏沒什麼好說的，有其餘語言的編程基礎的話都沒什麼問題。和Matlab的類似度比較大。這塊差異不是很大。具體以下：

         須要注意的一個是：5/2 等於2，5.0/2纔等於2.5。

 

###################################
### compute #######
# raw_input() get input from keyboard to string type
# So we should transfer to int type
# Some new support computing type:
# and or not in is < <= != == | ^ & << + - / % ~ **
print 'Please input a number:'
number = int(raw_input())
number += 1
print number**2 # ** means ^
print number and 1
print number or 1
print not number
5/2 # is 2
5.0/2 # is 2.5, should be noted

 

 

3、數據類型

一、數字

         一般的int, long,float,long等等都被支持。並且會看你的具體數字來定義變量的類型。以下：

 

###################################
### type of value #######
# int, long, float
# do not need to define the type of value, python will
# do this according to your value
num = 1   # stored as int type
num = 1111111111111   # stored as long int type
num = 1.0   # stored as float type
num = 12L # L stands for long type
num = 1 + 12j # j stands for complex type
num = '1' # string type

 

 

二、字符串

         單引號，雙引號和三引號均可以用來定義字符串。三引號能夠定義特別格式的字符串。字符串做爲一種序列類型，支持像Matlab同樣的索引訪問和切片訪問。

 

###################################
### type of string #######
num = "1" # string type
num = "Let's go" # string type
num = "He's \"old\"" # string type
mail = "Xiaoyi: \n hello \n I am you!"
mail = """Xiaoyi:
    hello
    I am you!
    """ # special string format
string = 'xiaoyi' # get value by index
copy = string[0] + string[1] + string[2:6] # note: [2:6] means [2 5] or[2 6)
copy = string[:4] # start from 1
copy = string[2:] # to end
copy = string[::1] # step is 1, from start to end
copy = string[::2] # step is 2
copy = string[-1] # means 'i', the last one
copy = string[-4:-2:-1] # means 'yoa', -1 step controls direction
memAddr = id(num) # id(num) get the memory address of num
type(num) # get the type of num

 

 

三、元組

         元組tuple用()來定義。至關於一個能夠存儲不一樣類型數據的一個數組。能夠用索引來訪問，但須要注意的一點是，裏面的元素不能被修改。

 

###################################
### sequence type #######
## can access the elements by index or slice
## include: string, tuple(or array? structure? cell?), list
# basis operation of sequence type
firstName = 'Zou'
lastName = 'Xiaoyi'
len(string) # the length
name = firstName + lastName # concatenate 2 string
firstName * 3 # repeat firstName 3 times
'Z' in firstName # check contain or not, return true
string = '123'
max(string)
min(string)
cmp(firstName, lastName) # return 1, -1 or 0

## tuple(or array? structure? cell?)
## define this type using ()
user = ("xiaoyi", 25, "male")
name = user[0]
age = user[1]
gender = user[2]
t1 = () # empty tuple
t2 = (2, ) # when tuple has only one element, we should add a extra comma
user[1] = 26 # error!! the elements can not be changed
name, age, gender = user # can get three element respectively
a, b, c = (1, 2, 3)

 

 

四、列表

         列表list用[]來定義。它和元組的功能同樣，不一樣的一點是，裏面的元素能夠修改。List是一個類，支持不少該類定義的方法，這些方法能夠用來對list進行操做。

 

## list type (the elements can be modified)
## define this type using []
userList = ["xiaoyi", 25, "male"]
name = userList[0]
age = userList[1]
gender = userList[2]
userList[3] = 88888 # error! access out of range, this is different with Matlab
userList.append(8888) # add new elements
"male" in userList # search
userList[2] = 'female' # can modify the element (the memory address not change)
userList.remove(8888) # remove element
userList.remove(userList[2]) # remove element
del(userList[1]) # use system operation api
## help(list.append)

################################
######## object and class ######
## object = property + method
## python treats anything as class, here the list type is a class,
## when we define a list "userList", so we got a object, and we use
## its method to operate the elements

 

 

五、字典

         字典dictionary用{}來定義。它的優勢是定義像key-value這種鍵值對的結構，就像struct結構體的功能同樣。它也支持字典類支持的方法進行建立和操做。

 

 

################################
######## dictionary type ######
## define this type using {}
item = ['name', 'age', 'gender']
value = ['xiaoyi', '25', 'male']
zip(item, value) # zip() will produce a new list:
# [('name', 'xiaoyi'), ('age', '25'), ('gender', 'male')]
# but we can not define their corresponding relationship
# and we can define this relationship use dictionary type
# This can be defined as a key-value manner
# dic = {key1: value1, key2: value2, ...}, key and value can be any type
dic = {'name': 'xiaoyi', 'age': 25, 'gender': 'male'}
dic = {1: 'zou', 'age':25, 'gender': 'male'}
# and we access it like this: dic[key1], the key as a index
print dic['name']
print dic[1]
# another methods create dictionary
fdict = dict(['x', 1], ['y', 2]) # factory mode
ddict = {}.fromkeys(('x', 'y'), -1) # built-in mode, default value is the same which is none
# access by for circle
for key in dic
    print key
    print dic[key]

# add key or elements to dictionary, because dictionary is out of sequence,
# so we can directly and a key-value pair like this:
dic['tel'] = 88888
# update or delete the elements
del dic[1] # delete this key
dic.pop('tel') # show and delete this key
dic.clear() # clear the dictionary
del dic # delete the dictionary
dic.get(1) # get the value of key
dic.get(1, 'error') # return a user-define message if the dictionary do not contain the key
dic.keys()
dic.values()
dic.has_key(key)
# dictionary has many operations, please use help to check out

 

 

4、流程控制

         在這塊，Python與其它大多數語言有個很是不一樣的地方，Python語言使用縮進塊來表示程序邏輯（其它大多數語言使用大括號等）。例如：

if age < 21:

    print("你不能買酒。")

    print("不過你能買口香糖。")

print("這句話處於if語句塊的外面。")

         這個代碼至關於c語言的：

if (age < 21)

{

    print("你不能買酒。")

    print("不過你能買口香糖。")

}

print("這句話處於if語句塊的外面。")

       能夠看到，Python語言利用縮進表示語句塊的開始和退出（Off-side規則），而非使用花括號或者某種關鍵字。增長縮進表示語句塊的開始（注意前面有個:號），而減小縮進則表示語句塊的退出。根據PEP的規定，必須使用4個空格來表示每級縮進（不清楚4個空格的規定如何，在實際編寫中能夠自定義空格數，可是要知足每級縮進間空格數相等）。使用Tab字符和其它數目的空格雖然均可以編譯經過，但不符合編碼規範。

       爲了使咱們本身編寫的程序能很好的兼容別人的程序，咱們最好仍是按規範來，用四個空格來縮減（注意，要麼都是空格，要是麼都製表符，千萬別混用）。

一、if-else

         If-else用來判斷一些條件，以執行知足某種條件的代碼。

 

################################
######## procedure control #####
## if else
if expression: # bool type and do not forget the colon
    statement(s) # use four space key

if expression:
statement(s) # error!!!! should use four space key

if 1<2:
    print 'ok, ' # use four space key
    print 'yeah' # use the same number of space key

if True: # true should be big letter True
    print 'true'

def fun():
    return 1

if fun():
    print 'ok'
else:
    print 'no'

con = int(raw_input('please input a number:'))
if con < 2:
    print 'small'
elif con > 3:
    print 'big'
else:
    print 'middle'

if 1 < 2:
    if 2 < 3:
        print 'yeah'
    else:
        print 'no'
    print 'out'
else:
    print 'bad'

if 1<2 and 2<3 or 2 < 4 not 0: # and, or, not
    print 'yeah'

 

 

二、for

         for的做用是循環執行某段代碼。還能夠用來遍歷咱們上面所提到的序列類型的變量。

 

################################
######## procedure control #####
## for
for iterating_val in sequence:
    statements(s)
# sequence type can be string, tuple or list

for i in "abcd":
    print i

for i in [1, 2, 3, 4]:
    print i

# range(start, end, step), if not set step, default is 1,
# if not set start, default is 0, should be noted that it is [start, end), not [start, end]
range(5) # [0, 1, 2, 3, 4]
range(1, 5) # [1, 2, 3, 4]
range(1, 10, 2) # [1, 3, 5, 7, 9]
for i in range(1, 100, 1):
    print i

# ergodic for basis sequence
fruits = ['apple', 'banana', 'mango']
for fruit in range(len(fruits)):
    print 'current fruit: ', fruits[fruit]

# ergodic for dictionary
dic = {1: 111, 2: 222, 5: 555}
for x in dic:
    print x, ': ', dic[x]

dic.items() # return [(1, 111), (2, 222), (5, 555)]
for key,value in dic.items(): # because we can: a,b=[1,2]
    print key, ': ', value
else:
    print 'ending'

################################
import time
# we also can use: break, continue to control process
for x in range(1, 11):
    print x
    time.sleep(1) # sleep 1s
    if x == 3:
        pass # do nothing
    if x == 2:
        continue
    if x == 6:
        break
    if x == 7:
        exit() # exit the whole program
    print '#'*50

 

 

三、while

         while的用途也是循環。它首先檢查在它後邊的循環條件，若條件表達式爲真，它就執行冒號後面的語句塊，而後再次測試循環條件，直至爲假。冒號後面的縮近語句塊爲循環體。

 

################################
######## procedure control #####
## while
while expression:
    statement(s)

while True:
    print 'hello'
    x = raw_input('please input something, q for quit:')
    if x == 'q':
        break
else:
    print 'ending'

 

 

四、switch

         其實Python並無提供switch結構，但咱們能夠經過字典和函數輕鬆的進行構造。例如：

 

#############################
## switch ####
## this structure do not support by python
## but we can implement it by using dictionary and function
## cal.py ##
#!/usr/local/python

from __future__ import division
# if used this, 5/2=2.5, 6/2=3.0

def add(x, y):
    return x + y
def sub(x, y):
    return x - y
def mul(x, y):
    return x * y
def div(x, y):
    return x / y

operator = {"+": add, "-": sub, "*": mul, "/": div}
operator["+"](1, 2) # the same as add(1, 2)
operator["%"](1, 2) # error, not have key "%", but the below will not
operator.get("+")(1, 2) # the same as add(1, 2)

def cal(x, o, y):
    print operator.get(o)(x, y)
cal(2, "+", 3)
# this method will effect than if-else

 

 

5、函數

一、自定義函數

         在Python中，使用def語句來建立函數：

 

################################
######## function #####
def functionName(parameters): # no parameters is ok
    bodyOfFunction

def add(a, b):
    return a+b # if we do not use a return, any defined function will return default None

a = 100
b = 200
sum = add(a, b)

##### function.py #####
#!/usr/bin/python
#coding:utf8  # support chinese
def add(a = 1, b = 2): # default parameters
    return a+b  # can return any type of data
# the followings are all ok
add()
add(2)
add(y = 1)
add(3, 4)

###### the global and local value #####
## global value: defined outside any function, and can be used
##              in anywhere, even in functions, this should be noted
## local value: defined inside a function, and can only be used
##              in its own function
## the local value will cover the global if they have the same name
val = 100 # global value
def fun():
    print val # here will access the val = 100
print val # here will access the val = 100, too

def fun():
    a = 100 # local value
    print a
print a # here can not access the a = 100

def fun():
    global a = 100 # declare as a global value
    print a

print a # here can not access the a = 100, because fun() not be called yet
fun()
print a # here can access the a = 100

############################
## other types of parameters
def fun(x):
    print x
# the follows are all ok
fun(10) # int
fun('hello') # string
fun(('x', 2, 3))  # tuple
fun([1, 2, 3])    # list
fun({1: 1, 2: 2}) # dictionary

## tuple
def fun(x, y):
    print "%s : %s" % (x,y) # %s stands for string
fun('Zou', 'xiaoyi')
tu = ('Zou', 'xiaoyi')
fun(*tu)    # can transfer tuple parameter like this

## dictionary
def fun(name = "name", age = 0):
    print "name: %s" % name
    print "age: " % age
dic = {name: "xiaoyi", age: 25} # the keys of dictionary should be same as fun()
fun(**dic) # can transfer dictionary parameter like this
fun(age = 25, name = 'xiaoyi') # the result is the same
## the advantage of dictionary is can specify value name

#############################
## redundancy parameters ####
## the tuple
def fun(x, *args): # the extra parameters will stored in args as tuple type
    print x
    print args
# the follows are ok
fun(10)
fun(10, 12, 24) # x = 10, args = (12, 24)

## the dictionary
def fun(x, **args): # the extra parameters will stored in args as dictionary type
    print x
    print args
# the follows are ok
fun(10)
fun(x = 10, y = 12, z = 15) # x = 10, args = {'y': 12, 'z': 15}

# mix of tuple and dictionary
def fun(x, *args, **kwargs):
    print x
    print args
    print kwargs
fun(1, 2, 3, 4, y = 10, z = 12) # x = 1, args = (2, 3, 4), kwargs = {'y': 10, 'z': 12}

 

 

二、Lambda函數

         Lambda函數用來定義一個單行的函數，其便利在於：

 

#############################
## lambda function ####
## define a fast single line function
fun = lambda x,y : x*y # fun is a object of function class
fun(2, 3)
# like
def fun(x, y):
    return x*y

## recursion
# 5=5*4*3*2*1, n!
def recursion(n):
    if n > 0:
        return n * recursion(n-1) ## wrong

def mul(x, y):
    return x * y
numList = range(1, 5)
reduce(mul, numList) # 5! = 120
reduce(lambda x,y : x*y, numList) # 5! = 120, the advantage of lambda function avoid defining a function

### list expression
numList = [1, 2, 6, 7]
filter(lambda x : x % 2 == 0, numList)
print [x for x in numList if x % 2 == 0] # the same as above
map(lambda x : x * 2 + 10, numList)
print [x * 2 + 10 for x in numList] # the same as above

 

 

三、Python內置函數

       Python內置了不少函數，他們都是一個個的.py文件，在python的安裝目錄能夠找到。弄清它有那些函數，對咱們的高效編程很是有用。這樣就能夠避免重複的勞動了。下面也只是列出一些經常使用的：

 

[python]  view plain copy

 

###################################
## built-in function of python ####
## if do not how to use, please use help()
abs, max, min, len, divmod, pow, round, callable,
isinstance, cmp, range, xrange, type, id, int()
list(), tuple(), hex(), oct(), chr(), ord(), long()

callable # test a function whether can be called or not, if can, return true
# or test a function is exit or not

isinstance # test type
numList = [1, 2]
if type(numList) == type([]):
    print "It is a list"
if isinstance(numList, list): # the same as above, return true
    print "It is a list"

for i in range(1, 10001) # will create a 10000 list, and cost memory
for i in xrange(1, 10001)# do not create such a list, no memory is cost

## some basic functions about string
str = 'hello world'
str.capitalize() # 'Hello World', first letter transfer to big
str.replace("hello", "good") # 'good world'
ip = "192.168.1.123"
ip.split('.') # return ['192', '168', '1', '123']
help(str.split)

import string
str = 'hello world'
string.replace(str, "hello", "good") # 'good world'

## some basic functions about sequence
len, max, min
# filter(function or none, sequence)
def fun(x):
    if x > 5:
        return True
numList = [1, 2, 6, 7]
filter(fun, numList) # get [6, 7], if fun return True, retain the element, otherwise delete it
filter(lambda x : x % 2 == 0, numList)
# zip()
name = ["me", "you"]
age = [25, 26]
tel = ["123", "234"]
zip(name, age, tel) # return a list: [('me', 25, '123'), ('you', 26, '234')]
# map()
map(None, name, age, tel) # also return a list: [('me', 25, '123'), ('you', 26, '234')]
test = ["hello1", "hello2", "hello3"]
zip(name, age, tel, test) # return [('me', 25, '123', 'hello1'), ('you', 26, '234', 'hello2')]
map(None, name, age, tel, test) # return [('me', 25, '123', 'hello1'), ('you', 26, '234', 'hello2'), (None, None, None, 'hello3')]
a = [1, 3, 5]
b = [2, 4, 6]
def mul(x, y):
    return x*y
map(mul, a, b) # return [2, 12, 30]
# reduce()
reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) # return ((((1+2)+3)+4)+5)

正則表達式：