With-blocks as a proper way to manage (open/close) file resources

usecase

The concern is documenting the control flow structure known as with-block that replaces the need to pair each open() with

1. usual pattern

• the pattern of working with the files where you

# 1. open a file
f = open(...)
# 2. work with the file
# ...
# 3. close a file
f.close()

• The close is important as it informs the operating system that the work with the file has been finished
• It closes the handle and releases the file for further use
• Also, it saves the changes — without closing, it is possible to lose data
• there may be pending writes buffered up that may not get written completely
• Or, when opening lots of files, the system may run out of resources
• The mechanism that pairs open() with close() is similar to garbage collector mechanisms in languages without memory management

2. enter with-block

• any objects that support he context-manager protocol — file objects are one of them
• it exploits the context-protocol nature of the file object
• it uses the with clause
• the aim is to get rid of the need to close the resource explicitly
• this is error-prone and even if it is not forgotten, one must use try-catch-finallly block to handle exceptions
• the with construct calls it for us

with EXP as VAR:
    BLOCK

3. zen of python

• this also resonates with the first aphorism of the zen of python: Beautiful is better than ugly which, here, is taking precedence over Explicit is better than implicit

4. comparative linguistics: this is similar to using in c-sharp

• the with-block has similar function as using in C#
• see my KB entry on C# > the File class + using statement implementing IDisposable

5. sources

• What is the python keyword “with” used for? — Stack Overflow