An example of context managers allocating and releasing resources precisely

python4pro_contextmanager.py

# requirement: create the txt file: zen_of_python.txt in the same directory that this python file

filename = 'zen_of_python.txt'
f = open(filename, 'r')
print("1st option 2 print content file")
print(f.read())
f.close()

# two related operations which you’d like to execute as a pair, with a
# block of code in between.
open_file = open(filename, 'r')
with open_file:
    print("2nd option 2 print content file")
    print(open_file.read())
"""
with EXPRESSION as TARGET:
    SUITE
@see: https://docs.python.org/3/reference/compound_stmts.html#the-with-statement    
unhandled error 
"""

with open(filename) as open_file:
    print("3rd option 2 print content file")
    """
    for line in open_file:
        print(line.rstrip())
    """
    print(open_file.read())


# The final solution, handling exceptions

class File(object):
    def __init__(self, file_name, method):
        try:
            self.file_obj = open(file_name, method)
        except Exception as e:
            print(f"Exception: {e}")

    def __enter__(self):
        return self.file_obj

    def __exit__(self, type, value, traceback):
        if type:
            print(f"Exception of type: {type} has been handled: {value}")
        self.file_obj.close()
        return True


with File('zen_of_python.txt', 'r') as open_file:
    # Exception here are managed in File.__exit__
    print("4th option 2 print content file")
    print(open_file.read())