Read and append to file python

Reading and Writing to text files in Python

Python provides inbuilt functions for creating, writing, and reading files. There are two types of files that can be handled in python, normal text files and binary files (written in binary language, 0s, and 1s).

• Text files: In this type of file, Each line of text is terminated with a special character called EOL (End of Line), which is the new line character (‘\n’) in python by default.
• Binary files: In this type of file, there is no terminator for a line, and the data is stored after converting it into machine-understandable binary language.

In this article, we will be focusing on opening, closing, reading, and writing data in a text file.

File Access Modes

Access modes govern the type of operations possible in the opened file. It refers to how the file will be used once its opened. These modes also define the location of the File Handle in the file. File handle is like a cursor, which defines from where the data has to be read or written in the file. There are 6 access modes in python.

1. Read Only (‘r’) : Open text file for reading. The handle is positioned at the beginning of the file. If the file does not exists, raises the I/O error. This is also the default mode in which a file is opened.
2. Read and Write (‘r+’): Open the file for reading and writing. The handle is positioned at the beginning of the file. Raises I/O error if the file does not exist.
3. Write Only (‘w’) : Open the file for writing. For the existing files, the data is truncated and over-written. The handle is positioned at the beginning of the file. Creates the file if the file does not exist.
4. Write and Read (‘w+’) : Open the file for reading and writing. For an existing file, data is truncated and over-written. The handle is positioned at the beginning of the file.
5. Append Only (‘a’): Open the file for writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.
6. Append and Read (‘a+’) : Open the file for reading and writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

How Files are Loaded into Primary Memory

There are two kinds of memory in a computer i.e. Primary and Secondary memory every file that you saved or anyone saved is on secondary memory cause any data in primary memory is deleted when the computer is powered off. So when you need to change any text file or just to work with them in python you need to load that file into primary memory. Python interacts with files loaded in primary memory or main memory through “file handlers” ( This is how your operating system gives access to python to interact with the file you opened by searching the file in its memory if found it returns a file handler and then you can work with the file ).

Opening a File

It is done using the open() function. No module is required to be imported for this function.

File_object = open(r"File_Name","Access_Mode")

The file should exist in the same directory as the python program file else, the full address of the file should be written in place of the filename. Note: The r is placed before the filename to prevent the characters in the filename string to be treated as special characters. For example, if there is \temp in the file address, then \t is treated as the tab character, and an error is raised of invalid address. The r makes the string raw, that is, it tells that the string is without any special characters. The r can be ignored if the file is in the same directory and the address is not being placed.

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File Handling in Python: Create, Open, Append, Read, Write

File handling is an integral part of programming. File handling in Python is simplified with built-in methods, which include creating, opening, and closing files.

While files are open, Python additionally allows performing various file operations, such as reading, writing, and appending information.

This article teaches you how to work with files in Python.

• Python 3 installed and set up.
• An IDE or code editor to write code.
• Access to a terminal to run the code (or run directly in an IDE).
• A text file for the examples.

Note: Follow one of our guides to install Python 3 for:

Opening Files in Python

The open() Python method is the primary file handling function. The basic syntax is:

file_object = open('file_name', 'mode')

The open() function takes two elementary parameters for file handling:

1. The file_name includes the file extension and assumes the file is in the current working directory. If the file location is elsewhere, provide the absolute or relative path.

2. The mode is an optional parameter that defines the file opening method. The table below outlines the different possible options:

Mode	Description
‘r’	Reads from a file and returns an error if the file does not exist (default).
‘w’	Writes to a file and creates the file if it does not exist or overwrites an existing file.
‘x’	Exclusive creation that fails if the file already exists.
‘a’	Appends to a file and creates the file if it does not exist or overwrites an existing file.
‘b’	Binary mode. Use this mode for non-textual files, such as images.
‘t’	Text mode. Use only for textual files (default).
‘+’	Activates read and write methods.

The mode must have exactly one create( x )/read( r )/write( w )/append( a ) method, at most one + . Omitting the mode defaults to ‘rt’ for reading text files.

Below is a table describing how each of the modes behave when invoked.

Behavior	Modes
Read	r , r+ , w+ , a+ , x+
Write	r+ , w , w+ , a , a+ , x+
Create	w , w+ , a , a+ , x , x+
Pointer Position Start	r , r+ , w , w+ , x , x+
Pointer Position End	a , a+
Truncate (clear contents)	w , w+
Must Exist	r , r+
Must Not Exist	x , x+

Read Mode

The read mode in Python opens an existing file for reading, positioning the pointer at the file’s start.

Note: If the file does not exist, Python throws an error.

To read a text file in Python, load the file by using the open() function:

The mode defaults to read text ( ‘rt’ ). Therefore, the following method is equivalent to the default:

To read files in binary mode, use:

Add + to open a file in read and write mode:

f = open("", "r+") # Textual read and write

f = open("", "rt+") # Same as above

f = open("", "rb+") # Binary read and write

In all cases, the function returns a file object and the characteristics depend on the chosen mode.

Note: Refer to our article How to Read From stdin in Python to learn more about using stdin to read files.

Write Mode

Write mode creates a file for writing content and places the pointer at the start. If the file exists, write truncates (clears) any existing information.

Warning: Write mode deletes existing content immediately. Check if a file exists before overwriting information by accident.

To open a file for writing information, use:

The default mode is text, so the following line is equivalent to the default:

To write in binary mode, open the file with:

Add + to allow reading the file:

f = open("", "w+") # Textual write and read

f = open("", "wt+") # Same as above

f = open("", "wb+") # Binary write and read

The open() function returns a file object whose details depend on the chosen modes.

Append Mode

Append mode adds information to an existing file, placing the pointer at the end. If a file does not exist, append mode creates the file.

Note: The key difference between write and append modes is that append does not clear a file’s contents.

Use one of the following lines to open a file in append mode:

f = open("", "at") # Same as above

f = open("", "ab") # Binary append

Add the + sign to include the read functionality.

Note: Learn how to append a string in Python.

Create Mode

Create mode (also known as exclusive create) creates a file only if it doesn’t exist, positioning the pointer at the start of the file.

Note: If the file exists, Python throws an error. Use this mode to avoid overwriting existing files.

Use one of the following lines to open a file in create mode:

f = open("", "xt") # Same as above

f = open("", "xb") # Binary create

Add the + sign to the mode include reading functionality to any of the above lines.

Reading Files in Python

After importing a file into an object, Python offers numerous methods to read the contents.

Use the read() method on the file object and print the result. For example:

f = open("file.txt") print(f.read(),end="")

Note: The print() function automatically adds a new empty line. To change this behavior, add the end=»» parameter to print() to remove the empty line.

The code prints the text file’s contents.

Read Parts of the File

Provide a number to the read() function to read only the specified number of characters:

f = open("file.txt") print(f.read(5))

The output prints the first five characters in the file.

Alternatively, use the readline() method to print only the first line of the file:

f = open("file.txt") print(f.readline())

Add an integer to the readline() function to print the specified number of characters without exceeding the first line.

Read Lines

To read lines and iterate through a file’s contents, use a for loop:

f = open("file.txt") for line in f: print(line, end="")

Alternatively, use the readlines() method on the file object:

f = open("file.txt") print(f.readlines())

The function returns the list of lines from the file stream.

Add an integer to the readlines() function to control the number of lines. For example:

f = open("file.txt") print(f.readlines(15))

The integer represents the character number, and the function returns the line where the character ends along with the previous lines.

Close Files

A file remains open until invoking the close() function. It’s good practice to close files no longer in use to avoid unpredictable file behavior and corrupted files.

To close a file, run the close() method on the file object:

An alternative way to ensure a file closes is to use the with statement. For example:

with open(""): file_contents = f.read() # Additional code here

The with statement automatically closes the file.

Note: Learn 3 methods on how to find list length in Python.

Deleting Files in Python

Removing files in Python requires establishing communication with the operating system. Import the os library and delete a file with the following:

import os os.remove("file.txt")

The file is no longer available. If the file does not exist, Python throws an error.

Python File Methods

Python offers various other functions when working with file objects. Below is a table that outlines all available processes and what they do.

Method	Description
close()	Flushes and closes the file object.
detach()	Separates buffer from text stream and returns the buffer.
fileno()	Returns the file’s descriptor if available.
flush()	Flushes the write buffer. Not available for read-only objects.
isatty()	Checks if a file stream is interactive.
read()	Read number of characters at most.
readable()	Checks if an object is readable.
readline()	Reads from the object until a newline or end of the file.
readlines()	Returns a list of lines from the file object, where is the approximate character number.
seek(, )	Changes the pointer position to relative to the .
seekable()	Checks if the file object supports random access.
tell()	Prints the current stream position.
truncate()	Resizes the file stream to (or current position if unstated) and returns the size.
write()	Writes to the file object and returns the written number of characters.
writable()	Checks whether the file object allows writing.
writelines()	Writes a of lines to the stream without a line separator.

You know how to handle files in Python after reading this guide. Try using a Python library such as Pandas to work with other file types.

For more Python tutorials refer to our article and find out how to add items to Python dictionary.

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