Question

I’m new to Python, so I’m not sure how I should do this.

I have a list of strings to write to a file. Each string needs to be preceded by a 32bit integer equal to the length of the string.

I need to have all the data that’s going to be written to the file before I write it to the file. In C#, I would store everything in a byte array before writing, but I have no clue what to do in Python. Should I use a list, or is there a better data type? How should the information be stored?

edit: an example of what it would look like is:

00 00 00 04 74 65 73 74

the four bytes of an integer in big endian, followed by the string.

Answer 1

You can use lambda expressions to easily create a new list according to the strings and your formatting requirements, like:

strings = ['abc', 'abcde', 'abcd', 'abcdefgh']
outputs = map(lambda x: "%d %s" % (len(x), x), strings) # ['3 abc', '5 abcde', '4 abcd', '8 abcdefgh']
f = open("file.out", 'w')
data = '\n'.join(outputs) # Concat all strings in list, separated by line break
f.write(data)
f.close()