import numpy as np
from tqdm import tqdm

filename = "~/test.dat"
nRows = 3702000
nCols = 2013
mmap = np.memmap(filename, shape=(nRows, nCols), dtype=np.float32, mode='w+')
chunkSize = 3000
offset = 0
data = np.ones((chunkSize, nCols))
for ii in tqdm(range(int(nRows / chunkSize))):
    mmap[offset:offset + chunkSize, :] = data
    offset += chunkSize
    if np.remainder(ii, 50):
        del mmap

mmap = np.memmap(filename, shape=(nRows, nCols), dtype=np.float32, mode='r+')