Python's
with operator lets you set up and tear down an object for use in a bock of code - typically useful for a file handle / resource accessor. Here's an example of it in use:
with day() as today:
print ("Today it is " + today)
It's set up using the
__enter__ method for the object, and released / torn down using the
__exit__ method. Here's the setting up of my "day" class for this example:
class day:
def __enter__(self):
daymeal = ("Beef Salad","Curried Beef","Sausages","Pasties","Fish","Sandwiches","Roast Beef")
self.food = daymeal[datetime.datetime.today().weekday()]
print ("serving " + self.food)
return self.food.upper()
def __exit__(self ,type, value, traceback):
print ("cleaning up from eating " + self.food)
Python's
in operator
when used with an if lets you check whether any value in a collection (list or tuple) is equal to the gieven value - i.e. check if a value's in a list, and with the use of a
not you can check if a value's missing (not present):
stuff = [20,"fifty",70,66]
if 55 in stuff: print (1)
if not 55 in stuff: print (3)
Python's
in operator
when used with a for iterates through a collection - placing a refernce to each item in the collection in turn into a target variable so that you can step through them in a loop:
for value in stuff:
print ("Value is {}".format(value))
Complete program showing all of these:
[here].
Sample output:
WomanWithCat:flask grahamellis$ python3 shin
2
3
serving Fish
Today it is FISH
cleaning up from eating Fish
None
None
None
Value is 20
Value is fifty
Value is 70
Value is 66
WomanWithCat:flask grahamellis$
Next Python courses start on 15th December, and further courses follow every 2 months next year. See
[here] for a full schedule.
"Learning to program in Python" is for newcomers to programming;
"Python Programming" for those with prior experience in another language.
(written 2015-10-16)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
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[383] Overloading of operators on standard objects in Python - (2005-07-19)
[477] Class, static and unbound variables - (2005-10-25)
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[831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
[903] Pieces of Python - (2006-10-23)
[964] Practical polymorphism in action - (2006-12-04)
[1146] __new__ v __init__ - python constructor alternatives? - (2007-04-14)
[1217] What are factory and singleton classes? - (2007-06-04)
[1517] Python - formatting objects - (2008-01-24)
[1644] Using a utility method to construct objects of different types - Python - (2008-05-17)
[1661] Equality, sameness and identity - Python - (2008-05-31)
[1819] Calling base class constructors - (2008-10-03)
[2368] Python - fresh examples of all the fundamentals - (2009-08-20)
[2409] TypeError: super() argument 1 must be type, not classobj (Python) - (2009-09-18)
[2485] How do I set up a constant in Python? - (2009-10-31)
[2693] Methods that run on classes (static methods) in Python - (2010-03-25)
[2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
[2720] Multiple inheritance in Python - complete working example - (2010-04-14)
[2722] Mixins example in Python - (2010-04-14)
[2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
[2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
[2889] Should Python classes each be in their own file? - (2010-07-27)
[2905] Defining static methods in Python - (2010-08-05)
[2994] Python - some common questions answered in code examples - (2010-10-10)
[3002] A list of special method and attribute names in Python - (2010-10-17)
[3442] A demonstration of how many Python facilities work together - (2011-09-16)
[3472] Static variables in functions - and better ways using objects - (2011-10-10)
[3524] Metaclasses (Python) and Metatables (Lua) - (2011-11-17)
[3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
[3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
[4028] Really Simple Class and Inheritance example in Python - (2013-03-04)
[4094] Python Properties - how and why - (2013-05-18)
[4344] Python base and inherited classes, test harness and unit testing - new examples - (2014-12-07)
[4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
[4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
[4410] A good example of recursion - a real use in Python - (2015-02-01)
[4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
[4450] Deciding whether to use parameters, conditional statements or subclasses - (2015-03-05)
[4649] Object and Static methods - what is the difference; example in Python 3 - (2016-02-17)
[4717] with in Python - examples of use, and of defining your own context - (2016-11-02)
[4718] Defining an object that is a modified standard type in Python - (2016-11-02)
[4719] Nesting decorators - (2016-11-02)
Y103 - Python - Conditionals and Loops [299] What - no switch or case statement? - (2005-05-03)
[353] Wimbledon Neck - (2005-06-20)
[657] The ternary operator in Python - (2006-03-25)
[668] Python - block insets help with documentation - (2006-04-04)
[788] New - Conditional expressions in Python 2.5 - (2006-07-01)
[835] Python - when to use the in operator - (2006-08-16)
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[1201] No switch in Python - (2007-05-23)
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[3083] Python - fresh examples from recent courses - (2010-12-11)
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[4210] If elif elif elif - multiway selection in Python - (2013-11-16)
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[4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
[4545] Method, Class, Module, Package - how to they relate in Python? - (2015-10-17)
[4713] Equality (in Python) - (2016-10-30)
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