必須先閱讀文件才能關閉文件？ Python

Question

這個程序只需要一個文件，刪除它，允許用戶輸入兩行放入空白文件，然後打印文件。

但是爲什麼我必須關閉文件對象並在顯示新添加的行之前重新打開它？

（注意該文件沒有在這個版本的代碼打印，但如果去掉＃的就正確執行。）

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

File對象默認緩衝;除非你編寫足夠的數據來填充緩衝區，否則在文件被刷新或關閉（隱式刷新）之前它不會寫入文件。這樣做是爲了避免大量（昂貴的）系統調用進行小寫操作。您可以通過致電fileobj.flush()直接強制刷新。

其他一些注意事項：如果目標是打開讀取/寫入和截斷文件，只需以模式'w+'打開，而不是'r+'後跟truncate()。其次，使用with語句，所以您不會意外無法關閉文件（通過省略close，或者由於拋出異常而繞過它）。示例：

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