If you only want to read the first 999,999 (non-header) rows:
read_csv(..., nrows=999999)
If you only want to read rows 1,000,000 ... 1,999,999
read_csv(..., skiprows=1000000, nrows=999999)
nrows : int, default None Number of rows of file to read. Useful for reading pieces of large files*
skiprows : list-like or integer Row numbers to skip (0-indexed) or number of rows to skip (int) at the start of the file
and for large files, you'll probably also want to use chunksize:
chunksize : int, default None Return TextFileReader object for iteration