Python_ Function _ File

function

1, Object-oriented Programming 2, process-oriented programming   # There is no return called Process 3, functional programming       # return returned is called a function  

how to pass a parameter

1, can define the way of the default parameters, location calls the way, and the location of the
def Run (x=1,y=2)     Print

2, the keyword call, regardless of location, will output 2,1 def test1 (x, y    ): Print (x)     Print (y) test1 (y=1,x=2)

PS: Key parameters cannot be in the middle

3, parameter group parameters (single *) accept the n positional parameters, cannot accept the keyword parameters, will eventually convert Cheng Yuanju def  Test1 (*args):    print  (Args,type (args))    for in  (args) :        print  (data,type (data)) test1 (1,3,4,5)  def test1 (x, *args):    Print  (x)    print  (args) test1 (1,2,3,4,5,6 )

4, Parameter group parameters (double *) received is a dictionary, the key must be passed in the Key=value format is the dictionary format
* *Kwargs parameter group must place def test1 (* *Kwargs)    :print  (Kwargs) test1 (Name= " Alex ", age=", sex="nan")

  Little Practice

defTest1 (x,y,z=1,*args,**Kwargs):Print(x)Print(y)Print(z)Print(args)Print(kwargs["name"]) test1 (1,2,3,4,5,6,name="Alex", age=" -", sex="nan") Output12Alex (4, 5, 6){'name':'Alex','Sex':'nan',' Age':' -'}

  local variables and global variablesA variable that takes effect inside a function is called a global variable, and a variable that takes effect globally is called a global variable. third, recursive function features1. There must be a clear end condition 2. Each entry to the next recursive layer should be reduced by 3 compared to the previous layer. Recursive hierarchy is not high, easy to cause memory overflow Iv. Higher-order functionsA variable can point to a function, which can receive a variable, and a function can receive another function as a parameter, a function called a higher order function.

def Add (x,y,f):     return f (x) + f (y)  = Add (3,-6, ABS)print(res)

eval can turn str into a dictionary

For example, in python3 with the input function, the incoming is the STR type, so that can be used User_input=eval (uesr_input) to turn into a dictionary again processing very well case{'Bakend':'www.old.org','Record':{'Server':'100.1.7.9','Weight': 20,'Maxconn': 30}}

Practice how to replace the modified character in a file because it is appended to the end of the file with a + r+, when it is necessary to modify the contents of a file only 2 methods 1, write to the memory of the modification, the modification is completed with Truncat empty the file and then write back 2, directly w+ create another file, Write something to another file, and then Os.rename os.remove Replace the file Case1 in-memory modification

def run ():
    f = open ("Tmp1.txt", "A +") #这里F打开文件后指针就已经去了末尾
    F.seek (0)                 #将指针指会开始位置, otherwise f.read can't read.
    m = F.read ()
    Print (m)
    F.seek (0) #读完后指针又去了末尾, put him back in the starting position.
    F.truncate (0) #截断文件, 0 indicates truncation from start position
    s = M.replace ("Test\nabc", "Xxxxxxxxxt")   #这里替换一个字符串
    F.write (s)         #写入字符串
Run ()

The content of Tmp1.txt is
Test
Abc
123

A + read-write way to open the file, if the file does not exist, create a file

the method of writing refers to appending with open ("Test.txt","A +") as F:f.write ("123\n")
The mode of reading refers to the with open ("Test.txt","A +") as F:f.seek (0) d=F.read () f.write ("123\n")Print(d)

The biggest difference between r+ and A + is that

r+ If you read and write first, the end is appended, if the direct write is overwrite

read first and write with open ("test.in"'r+') as F:    F.readline ()    f.write ("addition") hello1ok2byebye3addition 

The way of r+

R+ Way is read-write mode open

Read
With open ("Test.txt", "r+") as F:
Print (F.tell ())  #这里输出的位置是0
Print (F.read ())  #因为是0开始的所以这里会输出所有内容
Print (F.tell ())  #这里输出的是文件末尾

The way to write is to overwrite the original content, starting from 0 to write
With open ("Test2.txt", "r+") as F:

    Print (F.tell ())           #还是从0开始
    F.write ("aaaaaaaass\n")   #但是文件写入的方式是覆盖原有内容

Tell () How to judge a pointer

This assumes that the contents of the Test2.txt file are

123

With open ("test2.txt","r+") as F:    Print  (F.tell ())    d=f.read ()    print (len (d), F.tell ())

The output is as follows, that is, for this is the end of the null character, assuming you have a space to enter the count, the last Len length +1 is the position of your pointer

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Python_ Function _ File