3. Keyword argumentswith default values make it easy to add new behaviors to a function, especially when the function has existing callers.

4. Optional keyword arguments should always be passed by keyword instead of by position.

While Python's context managers are widely used, few understand the purpose behind their use. These statements, commonly used with reading and writing files, assist the application in conserving system memory and improve resource management by ensuring specific resources are only in use for certain processes.

A context manageris anobject thatis notified when a context (a block of code) startsand ends. You commonly use onewith thewith statement. It takes care of the notifying.

For example,file objects are context managers. When a context ends, thefileobjectis closed automatically:

>>>withopen(filename)as f:

>>>file_contents= f.read()

Anything that ends execution of the block causes the context manager's exit method to be called. This includes exceptions, and can be useful when an error causes you to prematurely exit from an open file or connection. Exiting a script without properly closing files/connections is a bad idea, that may cause data loss or other problems. By using a context manager you can ensure that precautions are always taken to prevent damage or loss in this way.

Itis also possible to write a context manager using generator syntax thanks to the```contextlib.contextmanager``` decorator:

>>>import contextlib

>>>@contextlib.contextmanager

...def context_manager(num):

...print('Enter')

...yield num+1

...print('Exit')

>>>with context_manager(2)as cm:

...print('Right in the middle with cm ={}'.format(cm))

Enter

Rightin the middlewithcm=3

Exit

The use of a Virtual Environmentis to test python codein encapsulated environmentsand to also avoid filling the base Python installationwith libraries we might usefor only one project.