在 python 中与 open() 一起使用后，seek(0) 如何无法倒带打开的文件

Question

当我试图在 python 中逐行打印文件内容时，我无法通过 f.seek(0) 倒带打开的文件如果文件是由 with open("file_name") as f: 打开的，则打印内容但是，如果我使用 open("file_name") as f: 我可以做到这一点然后 f.seek(0)

以下是我的代码

with open("130.txt", "r") as f:             #f is a FILE object
    print (f.read())                        #so f has method: read(), and f.read() will contain the newline each time 

f.seek(0)                             #This will Error!
with open("130.txt", "r") as f:       #Have to open it again, and I'm aware the indentation should change  
for line in f:                    
    print (line, end="")          

f = open("130.txt", "r")
f.seek(0)
for line in f:
    print(line, end="")

f.seek(0)                           #This time OK!
for line in f:
    print(line, end="")

我是python初学者，谁能告诉我为什么？

Answer 1

第一个f.seek(0)会抛出错误，因为

with open("130.txt", "r") as f:
    print (f.read())

将在块的末尾关闭文件（一旦文件被打印出来）

您需要执行以下操作：

with open("130.txt", "r") as f:
    print (f.read())

    # in with block
    f.seek(0)

Answer 2

with 的目的是在块结束时清理资源，在本例中包括关闭文件句柄。

您应该可以在 with 块中 .seek，但是：

with open('130.txt','r') as f:
  print (f.read())

  f.seek(0)
  for line in f:
    print (line,end='')

根据您的评论，with 在这种情况下是这样的语法糖：

f = open(...)
try:
  # use f
finally:
  f.close()

# f is still in scope, but the file handle it references has been closed

在 python 中与 open() 一起使用后，seek(0) 如何无法倒带打开的文件

How opened file cannot be rewind by seek(0) after using with open() in python

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