You can read your data as a text file instead of binary file.

Here's how:

file = open("/dev/rtlightsensor0", "r")
line = file.readline()
data = [int(each) for each in line.split())

Original answer:

You didn't describe your question clearly enough, but I'm guessing that you have four 32-bit (4 bytes) int in your file, which you want to read into your program.

os.read is a binary file read function, so the variable data you got is bytes instead of a list of numbers.

Python can't infer the length your number as it can be four 32-bit numbers, one 128-bit number, or something else. You need to define it explicitly.

There is also the issue of whether your data are big endian or little endian.

If your data doesn't come from a network communication, it's likely to be little endian. If you find the result from the following code is wrong (for example, unbelievably large), you can try to convert 'big' into 'little'.

You can finish your code like this:

dev = os.open("/dev/rtlightsensor0", os.0_RDWR)
raw_data = os.read(dev,16)
data = []
data.append(int.from_bytes(raw_data[0:4], 'little'))
data.append(int.from_bytes(raw_data[4:8], 'little'))
data.append(int.from_bytes(raw_data[8:12], 'little'))
data.append(int.from_bytes(raw_data[12:16], 'little'))
print(data)

However, DO NOT do it like that because it's really silly. If you can understand the code above, then you can write it better like this:

dev = os.open("/dev/rtlightsensor0", os.0_RDWR)
raw_data = os.read(dev, 16)
data = [int.from_bytes(raw_data[i * 4: (i + 1) * 4], 'little') for i in range(4)]
print(data)

By the way, it's not wise to read binary data like this. Generally speaking, the package numpy is recommended.

You want readlines (plural), not readline.
readline reads one line and returns it (so you wind up iterating over the characters in a string, one at a time), while readlines returns each line of the file, one after another.
Line-by-line iteration is the default for file objects (and StringIO objects), so you could just use

for x in buf:
    print(x)  # you may want to print x[:-1] to avoid extra newlines