- The two code blocks you gave are
not equivalent - The code you described as old way
of doing things has a serious bug:
in case opening the file fails you
will get a second exception in the
finally
clause becausef
is not
bound.
The equivalent old style code would be:
try:
f = open("file", "r")
try:
line = f.readline()
finally:
f.close()
except IOError:
<whatever>
As you can see, the with
statement can make things less error prone. In newer versions of Python (2.7, 3.1), you can also combine multiple expressions in one with
statement. For example:
with open("input", "r") as inp, open("output", "w") as out:
out.write(inp.read())
Besides that, I personally regard it as bad habit to catch any exception as early as possible. This is not the purpose of exceptions. If the IO function that can fail is part of a more complicated operation, in most cases the IOError should abort the whole operation and so be handled at an outer level. Using with
statements, you can get rid of all these try...finally
statements at inner levels.