需求
txt文件很大,難以打開,需要讀取n行看看數據格式。
開始
with open(f1_name, 'r') as f1:
contents1 = f1.readlines()[0:n_line]
with open(f2_name, 'w') as f2:
for line in contents1:
f2.write(line)
發現讀個10行需要6s(1G文件爲例,200G的話就慢死了)
後來
with open(f1_name, 'r') as f1:
while n_line > 0:
n_line = n_line - 1;
contents.append(f1.readline())
with open(f2_name, 'w') as f2:
for line in contents:
f2.write(line)
使用readline()取代readlines