Context Managers example will not return expected text

[FHeilmann]

>>> def start(env):
...     return '\begin{}'.format(env)

will cause start('center') to return egincenter. You need to escape the backslash and the curly braces like so:

>>> def start(env):
...     return '\\begin{{{}}}'.format(env)

same for end(env):

>>> def end(env):
...      return '\\end{{{}}}'.format(env)

edit:

the same applies for Function Based Context Managers and Class Based Context Managers

[mattharrison]

Fixed by your PR. THanks