目录不存在时的错误处理

Question

我有一种情况，我想将 MP3 存储在一个目录中，如果该目录不存在则创建该目录，如果无法创建该目录则退出程序。我读到这os.path.exists()对性能的影响比 更大os.makedirs()，因此考虑到这一点，我编写了以下代码：

try: 
    # If directory has not yet been created
    os.makedirs('Tracks')
    with open('Tracks/' + title + '.mp3', 'w') as mp3:
        mp3.write(mp3File.content)
        print '%s has been created.' % fileName

except OSError, e:
    # If directory has already been created and is accessible
    if os.path.exists('Tracks'):
        with open('Tracks/' + title + '.mp3', 'w') as mp3:
            mp3.write(mp3File.content)
            print '%s has been created.' % fileName

    else: # Directory cannot be created because of file permissions, etc. 
        sys.exit("Error creating 'Tracks' Directory. Cannot save MP3. Check permissions.")

这有道理吗？或者我应该坚持使用更干净但可能更昂贵的版本，即首先检查目录是否存在然后创建它？9/10次，目录就会在那里。

Answer 1

该try-except块可能更快，尽管正如 @t-8ch 所说，这并不重要。然而，它不必那么“不干净”：

try: 
    # try the thing you expect to work
    mp3 = open('Tracks/' + title + '.mp3', 'w')
except OSError, e:
    # exception is for the unlikely case
    os.makedirs('Tracks')
    mp3 = open('Tracks/' + title + '.mp3', 'w')

mp3.write(mp3File.content)
mp3.close()
print '%s has been created.' % fileName

如果你确实想try先创建目录，你可以这样做：

try: 
    # If directory has not yet been created
    os.makedirs('Tracks')
except OSError, e:
    # If directory has already been created or is inaccessible
    if not os.path.exists('Tracks')
        sys.exit("Error creating 'Tracks' Directory. Cannot save MP3. Check permissions.")
with open('Tracks/' + title + '.mp3', 'w') as mp3:
    mp3.write(mp3File.content)
    print '%s has been created.' % fileName