Question

该程序只需一个文件，删除它，允许用户输入两行放入空白文件，然后打印文件。

但为什么我必须关闭文件对象并在显示新添加的行之前重新打开它？

（请注意，此版本的代码中没有打印文件。但如果您删除＃＆＃39; s它将正确执行）

from sys import argv

sript, filename = argv

print "We will be buliding a new file from an %s" % filename
print "If you don't want to do this, hit CTRL_C"
print "If you do, hit and other key"

raw_input(">>>")

print "Oppening the file..."
file_ob = open(filename, "r+")
file_ob.truncate()

print "Now we will rewrite this file with the following line"
line1 = raw_input("The fist line will be :")
line2 = raw_input("The second line will be:")

print "Now we're put them into the file"
file_ob.write("\n\t>>>" + line1 + "\n\n\t>>>" + line2)

print "And now we will see what is in the file we just made"
print file_ob.read()

file_ob.close()

print "And now we will see what is in the file we just made"


#file_ob = open(filename, "r+")
#print file_ob.read()
#file_ob.close()

Answer 1

默认情况下缓冲文件对象;除非你写入足够的数据来填充缓冲区，否则它不会写入文件，直到文件被刷新或关闭（隐式刷新）。这样做是为了避免对小写进行大量（昂贵的）系统调用。您始终可以通过调用fileobj.flush()直接强制刷新。

其他一些注意事项：如果目标是打开读/写并截断文件，只需使用模式'w+'打开，而不是'r+'后跟truncate()。其次，使用with语句，因此您不会意外地无法关闭文件（省略close，或者由于抛出异常而绕过它）。例如：

with open(filename, "w+") as file_ob:
    # Don't need to truncate thanks to w+
    # Do writes/reads, with explicit flushes if needed
# When block exited by any means, file is flushed and closed automatically

在阅读之前必须关闭文件吗？蟒蛇

1 个答案: