First: use keyword with for the first time uncategorized solution for I Love Python! by hbczmxy - python coding challenges

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First: use keyword with for the first time solution in Uncategorized category for I Love Python! by hbczmxy

"""
Sharing this weird solution, really because I came across a "Share solution with something new" task that asked me to use "with" and share the new solution
"""

class Sample:
    def __init__(self, msg = "I love Python!"):
        self.msg = "I love Python!"
    
    def __enter__(self):
        print("I'm now in the context of Python! It's in __enter__")
        return self
    
    def i_love_python(self):
        return self.msg
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        print("I'm now out of the context of Python! It's in __exit__")

def get_sample():
    return Sample()
    
with get_sample() as sample:
    i_love_python = sample.i_love_python


if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    assert i_love_python() == "I love Python!"

Feb. 25, 2022

Comments:

hbczmxy on Feb. 25, 2022, 9:08 a.m.
2022-02-25 参考的网上资料：<a href="https://blog.csdn.net/u012609509/article/details/72911564?app_version=5.0.1&code=app_1562916241&uLinkId=usr1mkqgl919blen">Python 中 with用法及原理</a>

hbczmxy on Nov. 29, 2022, 8:18 a.m.
This is my first time using `with` keyword. And I cannot understand `with` keyword very well. <hr /> Here is the document about `with` keyword. ``` PS C:\Users\Admin> py -3 Python 3.10.4 (tags/v3.10.4:9d38120, Mar 23 2022, 23:13:41) [MSC v.1929 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. <blockquote> <blockquote> <blockquote> help('with') The "with" statement </blockquote> </blockquote> </blockquote> <hr /> The "with" statement is used to wrap the execution of a block with methods defined by a context manager (see section With Statement Context Managers). This allows common "try"…"except"…"finally" usage patterns to be encapsulated for convenient reuse. withstmt ::= "with" ( "(" withstmtcontents ","? ")" | withstmtcontents ) ":" suite withstmtcontents ::= withitem ("," withitem)* withitem ::= expression ["as" target] The execution of the "with" statement with one “item” proceeds as follows: <ol> <li>The context expression (the expression given in the "with_item") is evaluated to obtain a context manager.</li> <li>The context manager’s "enter()" is loaded for later use.</li> <li>The context manager’s "exit()" is loaded for later use.</li> <li>The context manager’s "enter()" method is invoked.</li> <li>If a target was included in the "with" statement, the return value from "enter()" is assigned to it. Note: The "with" statement guarantees that if the "enter()" method returns without an error, then "exit()" will always be called. Thus, if an error occurs during the assignment to the target list, it will be treated the same as an error occurring within the suite would be. See step 6 below.</li> <li>The suite is executed.</li> <li>The context manager’s "exit()" method is invoked. If an exception caused the suite to be exited, its type, value, and traceback are passed as arguments to "exit()". Otherwise, three "None" arguments are supplied. If the suite was exited due to an exception, and the return value from the "exit()" method was false, the exception is reraised. If the return value was true, the exception is suppressed, and execution continues with the statement following the "with" statement. If the suite was exited for any reason other than an exception, the return value from "exit()" is ignored, and execution proceeds at the normal location for the kind of exit that was taken.</li> </ol> The following code: with EXPRESSION as TARGET: SUITE is semantically equivalent to: manager = (EXPRESSION) enter = type(manager).enter exit = type(manager).exit value = enter(manager) hit_except = False try: TARGET = value SUITE except: hitexcept = True if not exit(manager, *sys.excinfo()): raise finally: if not hit_except: exit(manager, None, None, None) With more than one item, the context managers are processed as if multiple "with" statements were nested: with A() as a, B() as b: SUITE is semantically equivalent to: with A() as a: with B() as b: SUITE You can also write multi-item context managers in multiple lines if the items are surrounded by parentheses. For example: with ( A() as a, B() as b, ): SUITE Changed in version 3.1: Support for multiple context expressions. Changed in version 3.10: Support for using grouping parentheses to break the statement in multiple lines. See also: PEP 343 - The “with” statement The specification, background, and examples for the Python "with" statement. Related help topics: CONTEXTMANAGERS, EXCEPTIONS, yield <blockquote> <blockquote> > ``` </blockquote> </blockquote>

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