A file is closed by Python itself as the Python has a garbage collector, but we should properly close the file. An opened file in Python can be closed by the following command: CODE. F = open (“exp.txt”, encoding = ‘Utf-8’) close. Lerner Consulting Blog. Thoughts from Reuven Lerner about technology, business, and education. Menu and widgets. Search for: Categories. Book reviews (2) Business (18). It’s fine to let Python close files, either when the reference count to the file object drops to zero, or when Python exits.
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This chapter covers all the basic I/O functions available in Python. For more functions, please refer to standard Python documentation.
Printing to the Screen
The simplest way to produce output is using the print statement where you can pass zero or more expressions separated by commas. This function converts the expressions you pass into a string and writes the result to standard output as follows −
This produces the following result on your standard screen −
Reading Keyboard Input
Python provides two built-in functions to read a line of text from standard input, which by default comes from the keyboard. These functions are −
- raw_input
- input
The raw_input Function
The raw_input([prompt]) function reads one line from standard input and returns it as a string (removing the trailing newline).
This prompts you to enter any string and it would display same string on the screen. When I typed 'Hello Python!', its output is like this −
The input Function
The input([prompt]) function is equivalent to raw_input, except that it assumes the input is a valid Python expression and returns the evaluated result to you.
This would produce the following result against the entered input −
Opening and Closing Files
Until now, you have been reading and writing to the standard input and output. Now, we will see how to use actual data files.
Python provides basic functions and methods necessary to manipulate files by default. You can do most of the file manipulation using a file object.
The open Function
Before you can read or write a file, you have to open it using Python's built-in open() function. This function creates a file object, which would be utilized to call other support methods associated with it.
Syntax
Here are parameter details −
- file_name − The file_name argument is a string value that contains the name of the file that you want to access.
- access_mode − The access_mode determines the mode in which the file has to be opened, i.e., read, write, append, etc. A complete list of possible values is given below in the table. This is optional parameter and the default file access mode is read (r).
- buffering − If the buffering value is set to 0, no buffering takes place. If the buffering value is 1, line buffering is performed while accessing a file. If you specify the buffering value as an integer greater than 1, then buffering action is performed with the indicated buffer size. If negative, the buffer size is the system default(default behavior).
Here is a list of the different modes of opening a file −
The file Object Attributes
Once a file is opened and you have one file object, you can get various information related to that file.
Here is a list of all attributes related to file object −
Sr.No. | Attribute & Description |
---|---|
1 | file.closed Returns true if file is closed, false otherwise. |
2 | file.mode Returns access mode with which file was opened. |
3 | file.name Returns name of the file. |
4 | file.softspace Returns false if space explicitly required with print, true otherwise. |
Example
This produces the following result −
The close() Method
The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done.
Python automatically closes a file when the reference object of a file is reassigned to another file. It is a good practice to use the close() method to close a file.
Syntax
Example
This produces the following result −
Reading and Writing Files
The file object provides a set of access methods to make our lives easier. We would see how to use read() and write() methods to read and write files.
Python Does With Close File
The write() Method
The write() Beck's depression inventory pdf. method writes any string to an open file. It is important to note that Python strings can have binary data and not just text.
The write() method does not add a newline character ('n') to the end of the string −
Python With Doesn't Close File
Syntax
Python Close File If Open
Here, passed parameter is the content to be written into the opened file.
Example
The above method would create foo.txt file and would write given content in that file and finally it would close that file. If you would open this file, it would have following content.
The read() Method
The read() method reads a string from an open file. It is important to note that Python strings can have binary data. apart from text data.
Syntax
Here, passed parameter is the number of bytes to be read from the opened file. This method starts reading from the beginning of the file and if count is missing, then it tries to read as much as possible, maybe until the end of file.
Example
Let's take a file foo.txt, which we created above.
This produces the following result −
File Positions
The tell() method tells you the current position within the file; in other words, the next read or write will occur at that many bytes from the beginning of the file.
The seek(offset[, from]) method changes the current file position. The offset argument indicates the number of bytes to be moved. The from argument specifies the reference position from where the bytes are to be moved.
If from is set to 0, it means use the beginning of the file as the reference position and 1 means use the current position as the reference position and if it is set to 2 then the end of the file would be taken as the reference position.
Example
Let us take a file foo.txt, which we created above.
This produces the following result −
Renaming and Deleting Files
Python os module provides methods that help you perform file-processing operations, such as renaming and deleting files.
To use this module you need to import it first and then you can call any related functions.
The rename() Method
The rename() method takes two arguments, the current filename and the new filename.
Syntax
Example
Following is the example to rename an existing file test1.txt −
The remove() Method
You can use the remove() method to delete files by supplying the name of the file to be deleted as the argument.
Syntax
Example
Following is the example to delete an existing file test2.txt −
Directories in Python
All files are contained within various directories, and Python has no problem handling these too. The os module has several methods that help you create, remove, and change directories.
The mkdir() Method
You can use the mkdir() method of the os module to create directories in the current directory. You need to supply an argument to this method which contains the name of the directory to be created.
Syntax
Example
Following is the example to create a directory test in the current directory −
The chdir() Method
You can use the chdir() method to change the current directory. The chdir() method takes an argument, which is the name of the directory that you want to make the current directory.
Syntax
Example
Following is the example to go into '/home/newdir' directory −
The getcwd() Method
The getcwd() method displays the current working directory.
Syntax
Example
Following is the example to give current directory −
The rmdir() Method
The rmdir() method deletes the directory, which is passed as an argument in the method.
Before removing a directory, all the contents in it should be removed.
Syntax
Example
Following is the example to remove '/tmp/test' directory. It is required to give fully qualified name of the directory, otherwise it would search for that directory in the current directory.
File & Directory Related Methods
There are three important sources, which provide a wide range of utility methods to handle and manipulate files & directories on Windows and Unix operating systems. They are as follows −
- File Object Methods: The file object provides functions to manipulate files.
- OS Object Methods: This provides methods to process files as well as directories.