Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsOpen the file in binary mode and call read() to load its contents as Python bytes:
with open("data.bin", "rb") as file:
data = file.read()
Use bytearray(data) if you need to change individual bytes. For a large file, read and process bounded chunks instead of loading the entire file into memory.
Read the entire file as bytes
Use "rb" for read-binary mode. The "b" tells Python not to decode the file into text, so read() returns a bytes object containing the raw contents. The with block closes the file when the block ends.
with open("data.bin", "rb") as file:
data = file.read()
print(type(data)) # <class 'bytes'>
This is the straightforward choice when the whole file is small enough to keep in memory. Python’s built-in open() documentation describes binary file modes and their return type.
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Use pathlib for a concise whole-file read
If you do not need to keep an open file stream for additional operations, Path.read_bytes() reads and returns the file’s contents as bytes, opening and closing the file for the operation.
from pathlib import Path
data = Path("data.bin").read_bytes()
See the Path.read_bytes() documentation for the method details.
Convert to a mutable bytearray when needed
Python’s ordinary binary read returns immutable bytes. The built-in mutable type is bytearray; convert the data if you need to replace or edit byte values.
with open("data.bin", "rb") as file:
data = file.read()
mutable_data = bytearray(data)
if mutable_data:
mutable_data[0] = 0x41
The if check avoids indexing an empty file. A memoryview is another option when an API accepts buffer objects and you want to access binary data without making a copy. See the documentation for bytes, bytearray, and memoryview.
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Read a large file in chunks
A whole-file read retains the entire file in memory. To keep memory use bounded, read a chunk, handle it, and then continue. This example processes each chunk without storing all of them:
with open("large.bin", "rb") as file:
while chunk := file.read(64 * 1024):
process(chunk)
Replace process(chunk) with the operation your program needs to perform. The loop ends when read() returns an empty byte string at end-of-file. If you collect every chunk in a list and later join them, you will still need memory for the complete file.
Fill and reuse a mutable buffer with readinto()
If you need to read into storage you have already allocated, readinto() accepts a writable bytes-like buffer, such as a bytearray, and returns how many bytes it read. A call may read fewer bytes than the buffer’s capacity, so process only the portion indicated by the returned count.
buffer = bytearray(64 * 1024)
with open("large.bin", "rb") as file:
while count := file.readinto(buffer):
process(memoryview(buffer)[:count])
This reuses the same buffer on each iteration. A downstream function that needs to retain the data beyond the next read should make its own copy. See Python’s I/O stream documentation for read(), readinto(), and in-memory binary streams such as io.BytesIO.
Binary mode versus text mode
Text mode, selected by "r", decodes file bytes into a Python string. Binary mode, selected by "rb", returns bytes without decoding. Use binary mode for arbitrary binary data, or when you deliberately need the underlying bytes of a text-formatted file. If you later want to interpret those bytes as text, decode them separately using the encoding you know the file uses.
As the Python tutorial puts it: “Binary mode data is read and written as bytes objects.” See the file-reading and writing tutorial.
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