Line Reader

line_reader.py

class LineReader:
    """
    Read a static file with smart line access.

    WARNING: This implementation assumes that the file does not change between
    calls of the `clear` function and never checks for valid file handlers.
    """

    def __init__(self, file_handle=None, cache=None, offsets=None):
        """Initialize the LineReader."""
        self.file_handle = file_handle
        self.cache = cache if cache else {}
        self.offsets = offsets if offsets else []

    def clear(self):
        """Clear line cache and offset table."""
        self.cache.clear()
        self.offsets.clear()

    def get(self, n):
        """
        Get line as fast as possible, using the line cache and offset table.
        """
        line = self.cache.get(n)
        if line is not None or n < 0:
            return line
        offset_index = len(self.offsets) - 1
        if offset_index >= n:
            self.file_handle.seek(self.offsets[n])
            self.cache[n] = self.file_handle.readline()[:-1]
            return self.cache[n]
        if not self.offsets:
            self.offsets.append(0)
            offset_index = 0
        self.file_handle.seek(self.offsets[-1])
        for index, line in enumerate(self.file_handle, start=offset_index):
            self.offsets.append(self.offsets[-1] + len(line))
            if index == n:
                self.cache[n] = line[:-1]
                return self.cache[n]
        return None