Python file operations

Python_files_operations

Files, file objects

Open (name [, mode [, BufSize]]) Eg:file = "Data.txt" f = open (file, ' r ') F = open (file, ' W ')

• ' R ': Read
• ' W ': Write
• ' A ': Append
• ' RB ': Write binary, where files in Unix can be binary, so use ' RB '
• ' U ' or ' RU ': provides universal support for line breaks and can write files executed across platforms

Line break is ' \ r \ n ' in Windows, ' \ n ' in Unix

Methods

• F.read ([n]): read at the most n bytes
• F.readline ([n]): reads up to N per line
• F.readlines ([size])
• F.write (String): Writes a string to F
• F.writelines (lines)
• F.close ()
• F.tell (): Returns the Cur pointer
• F.seek ()

Some properties of the file object:

• F.closed: Returns False if the file is turned on
• F.mode
• F.name
• F.softspace
• F.newlines
• F.encoding

How to traverse Files:

# method 1while True: Line    = F.readline ()        If the line:            break# method 2for line in F:    # Process Line

Sys.stdin, Sys.stout, Sys.stderr

StdIn maps to the user's keyboard input, stdout and stderr output text to the screen eg:

Import Syssys.stdout.write ("Enter your Name:") name = Sys.stdin.readline ()

The above equivalence and Raw_input ():

Name = Raw_input ("Enter your Name:")

Raw_input does not include subsequent newline characters when read, which differs from Stdin.readline ()

The print statement can use ', ' to indicate that there is no output line break:

Print 1, 2, 3, 4# equivalent with print 1,2,pirnt 3,4

Formatted output

Print "The values are%d%7.5f%s"% (x, y, z) print "The values is {0:d} {1:7.5f} {2}". Format (z/y)

Python3 inside, print as a function of the form, as follows:

Pirnt ("The values are", X, Y, Z, end = ")

If you want to redirect the output to a file, the Python2 is as follows:

f = open ("Output.txt", "W") print >>f, "Hello World" ... f.close ()

Inside the Python3, you can do this directly via the print () function:

Print ("The values are", x,x,z, file = f)

You can also set the delimiter between elements:

Print ("The values are", X, Y, z, Sep = ', ')

The use of "'

"Can be used to do some formatted output, such as:

form = "" "Dear% (name) s,please send back my% (item) s or pay me $% (amount) 0.2f.                                Sincerely yours,                                Joe Python User "" "Print form% {               ' name ': ' Mr Bush ',              ' item ': ' Blender ',              ' amount ': 50.00 ,}

will be output

Dear Mr bush,please send back my blender or pay me $50.00.                                Sincerely yours,                                Joe Python User

Note that the first line after the/means the first line of the newline character, or in front of the output more than a blank line. () The keywords inside will be replaced.

The same effect can be achieved with the format () function:

form = ' Dear {name}s,please send back my {item}s or pay me ${amount:0.2f}.                                Sincerely yours,                                Joe Python User "Print form.format (name =" Jack ", item =" Blender ", amount = 50)

and the template function inside the string:

Import Stringform = string. Template ("" "Dear $name, please send the back to my $item or pay me $amount.                    Sincerely yours,                    Joe Python User "" ") print Form.substitute ({' name ': ' Mr Bush ', ' Item ': ' Blender ', ' Amount ': '%0.2f '% 50.0})

Here, use $ to indicate what will be replaced.

Python file operations