Python open line buffering

Open a File in Python

In this tutorial, you’ll learn how to open a file in Python.

The data can be in the form of files such as text, csv, and binary files. To extract data from these files, Python comes with built-in functions to open a file and then read and write the file’s contents.

After reading this tutorial, you can learn: –

• How to open a file in Python using both relative and absolute path
• Different file access modes for opening a file
• How to open a file for reading, writing, and appending.
• How to open a file using the with statement
• Importance of closing a file

Table of contents

Access Modes for Opening a file

The access mode parameter in the open() function primarily mentions the purpose of opening the file or the type of operation we are planning to do with the file after opening. in Python, the following are the different characters that we use for mentioning the file opening modes.

# Opening the file with absolute path fp = open(r'E:\demos\files\sample.txt', 'r') # read file print(fp.read()) # Closing the file after reading fp.close() # path if you using MacOs # fp = open(r"/Users/myfiles/sample.txt", "r")

Welcome to PYnative.com This is a sample.txt

Opening a File with Relative Path

A relative path is a path that starts with the working directory or the current directory and then will start looking for the file from that directory to the file name.

For example, reports/sample.txt is a relative path. In the relative path, it will look for a file into the directory where this script is running.

# Opening the file with relative path try: fp = open("sample.txt", "r") print(fp.read()) fp.close() except FileNotFoundError: print("Please check the path.")

Handling the FileNotFoundError

In case we are trying to open a file that is not present in the mentioned path then we will get a FileNotFoundError .

fp = open(r'E:\demos\files\reports.txt', 'r') print(f.read())

FileNotFoundError: [Errno 2] No such file or directory: 'E:\demos\files\reports.txt'

We can handle the file not found error inside the try-except block. Let us see an example for the same. Use except block to specify the action to be taken when the specified file is not present.

try: fp = open(r'E:\PYnative\reports\samples.txt', 'r') print(fp.read()) fp.close() except IOError: print("File not found. Please check the path.") finally: print("Exit")

File not found. Please check the path. Exit

File open() function

Python provides a set of inbuilt functions available in the interpreter, and it is always available. We don’t have to import any module for that. We can open a file using the built-in function open().

Syntax of the file open() function

open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

It return the file object which we can sue to read or write to a file.

Let us see the parameters we can pass to the open() function to enhance the file operation.

Closing a File

We need to make sure that the file will be closed properly after completing the file operation. It is a bad practice to leave your files open.

In Python, It is very important to close a file once the job is done mainly for the following reasons: –

• It releases the resources that have been tied up with the file. By this space in the RAM can be better utilized and ensures a better performance.
• It ensures better garbage collection.
• There is a limit to the number of open files in an application. It is always better to close the file to ensure that the limit is not crossed.
• If you open the file in write or read-write mode, you don’t know when data is flushed.

A file can be closed just by calling the close() function as follows.

# Opening the file to read the contents f = open("sample2.txt", "r") print(f.read()) # Closing the file once our job is done f.close()

Opening file using with statement

We can open a file using the with statement along with the open function. The general syntax is as follows.

with open(__file__, accessmode) as f:

The following are the main advantages of opening a file using the with statement

• The with statement simplifies exception handling by encapsulating common preparation and cleanup tasks.
• This also ensures that a file is automatically closed after leaving the block.
• As the file is closed automatically it ensures that all the resources that are tied up with the file are released.

Let us see how we can the with statement for opening a file with an example. Consider there are two files ‘sample.txt’ and ‘sample2.txt’ and we want to copy the contents of the first file to the second.

# Opening file with open('sample.txt', 'r', encoding='utf-8') as infile, open('sample2.txt', 'w') as outfile: # read sample.txt an and write its content into sample2.txt for line in infile: outfile.write(line) # Opening the file to read the contents f = open("Sample2.txt", "r") print(f.read()) f.close()

Welcome to PYnative.com File created to demonstrate file handling in Python

Here we can see that the contents of the sample2.txt has been replaced by the contents of sample.txt.

Creating a new file

We can create a new file using the open() function by setting the x mode. This method will ensure that the file doesn’t already exist and then create a new file. It will raise the FileExistsError if the file already exists.

Example: Creating a new file.

try: # Creating a new file with open("sample3.txt", "x") as fp: fp.write("Hello World! I am a new file") # reading the contents of the new file fp = open("sample3.txt", "r") print(fp.read()) except FileExistsError: print("The file already exists")

Hello World! I am a new file

Opening a File for multiple operations

In Python, we can open a file for performing multiple operations simultaneously by using the ‘+’ operator. When we pass r+ mode then it will enable both reading and writing options in the file. Let us see this with an example.

with open("Sample3.txt", "r+") as fp: # reading the contents before writing print(fp.read()) # Writing new content to this file fp.write("\nAdding this new content")

Opening a Binary file

Binary files are basically the ones with data in the Byte format (0’s and 1’s). This generally doesn’t contain the EOL(End of Line) so it is important to check that condition before reading the contents of the file.

We can open and read the contents of the binary file as below.

with open("sample.bin", "rb") as f: byte_content = f.read(1) while byte_content: # Printing the contents of the file print(byte_content) 

Summary

In this tutorial, we have covered how to open a file using the different access modes. Also, we learned the importance of opening a file using the ‘with’ statement.

Did you find this page helpful? Let others know about it. Sharing helps me continue to create free Python resources.

About Vishal

I’m Vishal Hule, Founder of PYnative.com. I am a Python developer, and I love to write articles to help students, developers, and learners. Follow me on Twitter

Related Tutorial Topics:

Python Exercises and Quizzes

Free coding exercises and quizzes cover Python basics, data structure, data analytics, and more.

• 15+ Topic-specific Exercises and Quizzes
• Each Exercise contains 10 questions
• Each Quiz contains 12-15 MCQ

Источник

open¶

‘r’ open for reading (default) ‘w’ open for writing, truncating the file first ‘a’ open for writing, appending to the end of the file if it exists ‘b’ binary mode ‘t’ text mode (default) ‘+’ open a disk file for updating (reading and writing) ‘U’ universal newlines mode (for backwards compatibility; should not be used in new code)

‘0’ to switch buffering off (only allowed in binary mode) ‘1’ to select line buffering (only usable in text mode) ‘integer > 1’ to indicate the size of a fixed-size chunk buffer

Return Value¶

Time Complexity¶

Remarks¶

The most commonly-used values of mode are ‘r’ for reading, ‘w’ for writing (truncating the file if it already exists), and ‘a’ for appending (which on some Unix systems means that all writes append to the end of the file regardless of the current seek position). If mode is omitted, it defaults to ‘r’. The default is to use text mode, which may convert ‘n’ characters to a platform-specific representation on writing and back on reading. Thus, when opening a binary file, you should append ‘b’ to the mode value to open the file in binary mode, which will improve portability. (Appending ‘b’ is useful even on systems that don’t treat binary and text files differently, where it serves as documentation.) See below for more possible values of mode.

The optional buffering argument specifies the file’s desired buffer size: 0 means unbuffered, 1 means line buffered, any other positive value means use a buffer of (approximately) that size (in bytes). A negative buffering means to use the system default, which is usually line buffered for tty devices and fully buffered for other files. If omitted, the system default is used.

Modes ‘r+’, ‘w+’ and ‘a+’ open the file for updating (note that ‘w+’ truncates the file). Append ‘b’ to the mode to open the file in binary mode, on systems that differentiate between binary and text files; on systems that don’t have this distinction, adding the ‘b’ has no effect.

In addition to the standard fopen() values mode may be ‘U’ or ‘rU’. Python is usually built with universal newlines support; supplying ‘U’ opens the file as a text file, but lines may be terminated by any of the following: the Unix end-of-line convention ‘n’, the Macintosh convention ‘r’, or the Windows convention ‘rn’. All of these external representations are seen as ‘n’ by the Python program. If Python is built without universal newlines support a mode with ‘U’ is the same as normal text mode. Note that file objects so opened also have an attribute called newlines which has a value of None (if no newlines have yet been seen), ‘n’, ‘r’, ‘rn’, or a tuple containing all the newline types seen.

Python enforces that the mode, after stripping ‘U’, begins with ‘r’, ‘w’ or ‘a’.

Python provides many file handling modules including fileinput, os, os.path, tempfile, and shutil.

Example¶

>>> open('C:\\alice_in_wonderland.txt') >>> alice = open(r'C:\alice_in_wonderland.txt', 'r+') >>> alice.readline() " ALICE'S ADVENTURES IN WONDERLAND\n" 

Источник