File modes reference

When opening files in Python, the mode parameter determines how the file is opened and what operations are available. This reference covers all file modes and their combinations.

Mode overview

Mode	Access	Creates file	Truncates	Position	Description
"r"	Read only	No	No	Start	Open for reading (default)
"w"	Write only	Yes	Yes	Start	Open for writing (creates or truncates)
"a"	Write only	Yes	No	End	Open for appending
"x"	Write only	Yes (error if exists)	No	Start	Exclusive creation
"r+"	Read + Write	No	No	Start	Open for reading and writing
"w+"	Read + Write	Yes	Yes	Start	Open for writing and reading
"a+"	Read + Write	Yes	No	End	Open for appending and reading
"rb"	Read only (binary)	No	No	Start	Read binary data
"wb"	Write only (binary)	Yes	Yes	Start	Write binary data
"ab"	Append only (binary)	Yes	No	End	Append binary data
"xb"	Write only (binary)	Yes (error if exists)	No	Start	Exclusive creation (binary)
"r+b"	Read + Write (binary)	No	No	Start	Read and write binary data
"w+b"	Read + Write (binary)	Yes	Yes	Start	Write and read binary data
"a+b"	Read + Write (binary)	Yes	No	End	Append and read binary data

Mode characters

Access modes

• "r" -- Read. The file must exist. This is the default mode.
• "w" -- Write. Creates the file if it does not exist. Truncates (empties) the file if it already exists.
• "a" -- Append. Creates the file if it does not exist. Writes are always added to the end of the file.
• "x" -- Exclusive creation. Creates a new file. Raises FileExistsError if the file already exists.

Modifier characters

• "b" -- Binary mode. Data is read and written as bytes objects. Do not specify encoding in binary mode.
• "t" -- Text mode (default). Data is read and written as str objects. Specify encoding for consistent behaviour.
• "+" -- Update mode. Opens the file for both reading and writing.

Detailed mode descriptions

Read mode ("r")

When to use: reading existing text files.

with open("data.txt", "r", encoding="utf-8") as f:
    content = f.read()

• The file must already exist -- FileNotFoundError is raised otherwise
• The file position starts at the beginning
• Only read operations are available

Write mode ("w")

When to use: creating a new file or replacing the contents of an existing file.

with open("output.txt", "w", encoding="utf-8") as f:
    f.write("New content\n")

• Creates the file if it does not exist
• Truncates the file if it already exists -- all existing content is deleted
• The file position starts at the beginning
• Only write operations are available

Warning

Write mode deletes all existing content. If you want to add to a file, use append mode ("a") instead.

Append mode ("a")

When to use: adding content to the end of an existing file, or creating a new file if it does not exist.

with open("log.txt", "a", encoding="utf-8") as f:
    f.write("New log entry\n")

• Creates the file if it does not exist
• Does not truncate the file
• The file position starts at the end
• All writes go to the end of the file, regardless of calls to seek()

Exclusive creation mode ("x")

When to use: creating a new file safely, ensuring you do not accidentally overwrite an existing file.

try:
    with open("output.txt", "x", encoding="utf-8") as f:
        f.write("Safely created\n")
except FileExistsError:
    print("File already exists.")

• Creates a new file
• Raises FileExistsError if the file already exists
• Only write operations are available

Read-write mode ("r+")

When to use: reading and modifying an existing file.

with open("data.txt", "r+", encoding="utf-8") as f:
    content = f.read()
    f.seek(0)
    f.write("Modified content\n")

• The file must already exist
• The file position starts at the beginning
• Both read and write operations are available
• Does not truncate the file

Write-read mode ("w+")

When to use: creating a new file (or replacing an existing one) that you want to both write to and read from.

with open("data.txt", "w+", encoding="utf-8") as f:
    f.write("Hello\n")
    f.seek(0)
    content = f.read()

• Creates the file if it does not exist
• Truncates the file if it already exists
• Both read and write operations are available

Append-read mode ("a+")

When to use: appending to a file while also being able to read its contents.

with open("log.txt", "a+", encoding="utf-8") as f:
    f.write("New entry\n")
    f.seek(0)
    content = f.read()

• Creates the file if it does not exist
• Does not truncate the file
• The file position starts at the end
• Both read and write operations are available

Binary read mode ("rb")

When to use: reading non-text files such as images, PDFs, or compressed archives.

with open("image.png", "rb") as f:
    data = f.read()

• Works with bytes objects, not strings
• Do not specify encoding
• No newline translation

Binary write mode ("wb")

When to use: writing non-text data.

with open("output.bin", "wb") as f:
    f.write(b"\x89PNG\r\n\x1a\n")

• Works with bytes objects
• Creates the file if it does not exist
• Truncates the file if it already exists

Text mode versus binary mode

Feature	Text mode	Binary mode
Data type	str	bytes
Encoding	Specified (for example, "utf-8")	Not applicable
Newline translation	Yes (platform-dependent)	No
Use for	Text files (.txt, .csv, .json, .xml)	Images, PDFs, audio, compressed archives

Newline handling

In text mode, Python handles newlines differently depending on the platform:

• Reading: platform-specific line endings (such as \r\n on Windows) are translated to \n
• Writing: \n is translated to the platform-specific line ending

The newline parameter in open() controls this behaviour:

Value	Reading behaviour	Writing behaviour
None (default)	Universal newline mode – all line endings become \n	\n is translated to the platform default
""	No translation – all line endings are returned as-is	No translation -- \n is written as-is
"\n"	Only \n is recognised as a line ending	No translation
"\r\n"	Only \r\n is recognised as a line ending	\n is written as \r\n

For CSV files, always use newline="" to prevent double newlines.

Decision guide

Task	Recommended mode
Read a text file	"r"
Write a new text file (or replace existing)	"w"
Add to the end of a text file	"a"
Create a new file safely (no overwrite)	"x"
Read and modify a text file	"r+"
Read an image, PDF, or binary file	"rb"
Write binary data	"wb"
Read a CSV file	"r" with newline=""
Write a CSV file	"w" with newline=""

See also

• open() function reference
• pathlib quick reference
• Official Python documentation for open()