Further Object-Oriented Programming in Java

Encoding UPC-A in Java Further Object-Oriented Programming
Further Object-Oriented Programming
UCC - 12 Printer In Java
Using Barcode creator for Java Control to generate, create UPC Code image in Java applications.
It is only necessary to use contextlibnested() for Python 30; from Python 31 this function is deprecated because Python 31 can handle multiple context managers in a single with statement Here is the same example again omitting irrelevant lines but this time for Python 31:
Paint Barcode In Java
Using Barcode drawer for Java Control to generate, create bar code image in Java applications.
try: with open(source) as fin, open(target, "w") as fout: for line in fin:
Bar Code Recognizer In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
Using this syntax keeps context managers and the variables they are associated with together, making the with statement much more readable than if we were to nest them or to use contextlibnested() It isn t only le objects that are context managers For example, several threading-related classes used for locking are context managers Context managers can also be used with decimalDecimal numbers; this is useful if we want to perform some calculations with certain settings (such as a particular precision) in effect If we want to create a custom context manager we must create a class that provides two methods: __enter__() and __exit__() Whenever a with statement is used on an instance of such a class, the __enter__() method is called and the return value is used for the as variable (or thrown away if there isn t one) When control leaves the scope of the with statement the __exit__() method is called (with details of an exception if one has occurred passed as arguments) Suppose we want to perform several operations on a list in an atomic manner that is, we either want all the operations to be done or none of them so that the resultant list is always in a known state For example, if we have a list of integers and want to append an integer, delete an integer, and change a couple of integers, all as a single operation, we could write code like this:
UPC Symbol Generator In Visual Studio .NET
Using Barcode generator for ASP.NET Control to generate, create UPC-A Supplement 5 image in ASP.NET applications.
try: with AtomicList(items) as atomic: atomicappend(58289) del atomic[3] atomic[8] = 81738 atomic[index] = 38172 except (AttributeError, IndexError, ValueError) as err: print("no changes applied:", err)
GTIN - 12 Generator In .NET Framework
Using Barcode drawer for VS .NET Control to generate, create UPC Symbol image in .NET applications.
Threading
Generating Code 3 Of 9 In Java
Using Barcode maker for Java Control to generate, create Code 3 of 9 image in Java applications.
439
Bar Code Creator In Java
Using Barcode printer for Java Control to generate, create bar code image in Java applications.
If no exception occurs, all the operations are applied to the original list (items), but if an exception occurs, no changes are made at all Here is the code for the AtomicList context manager:
Bar Code Creation In Java
Using Barcode generation for Java Control to generate, create bar code image in Java applications.
class AtomicList: def __init__(self, alist, shallow_copy=True):
Barcode Encoder In Java
Using Barcode encoder for Java Control to generate, create barcode image in Java applications.
8 Advanced Programming Techniques
Draw UPC A In Java
Using Barcode printer for Java Control to generate, create Universal Product Code version A image in Java applications.
selforiginal = alist selfshallow_copy = shallow_copy def __enter__(self): selfmodified = (selforiginal[:] if selfshallow_copy else copydeepcopy(selforiginal)) return selfmodified def __exit__(self, exc_type, exc_val, exc_tb): if exc_type is None: selforiginal[:] = selfmodified
Making EAN 8 In Java
Using Barcode printer for Java Control to generate, create EAN8 image in Java applications.
Shallow and deep copying 146
GS1 - 12 Decoder In Visual Studio .NET
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
When the AtomicList object is created we keep a reference to the original list and note whether shallow copying is to be used (Shallow copying is ne for lists of numbers or strings; but for lists that contain lists or other collections, shallow copying is not suf cient) Then, when the AtomicList context manager object is used in the with statement its __enter__() method is called At this point we copy the original list and return the copy so that all the changes can be made on the copy Once we reach the end of the with statement s scope the __exit__() method is called If no exception occurred the exc_type ( exception type ) will be None and we know that we can safely replace the original list s items with the items from the modi ed list (We cannot do selforiginal = selfmodified because that would just replace one object reference with another and would not affect the original list at all) But if an exception occurred, we do nothing to the original list and the modi ed list is discarded The return value of __exit__() is used to indicate whether any exception that occurred should be propagated A True value means that we have handled any exception and so no propagation should occur Normally we always return False or something that evaluates to False in a Boolean context to allow any exception that occurred to propagate By not giving an explicit return value, our __exit__() returns None which evaluates to False and correctly causes any exception to propagate Custom context managers are used in 11 to ensure that socket connections and gzipped les are closed, and some of the threading modules context managers are used in 10 to ensure that mutual exclusion locks are unlocked You ll also get the chance to create a more generic atomic contex manager in this chapter s exercises
Code 128 Code Set B Printer In C#.NET
Using Barcode printer for .NET Control to generate, create Code 128 Code Set A image in .NET framework applications.
Barcode Generation In Visual Studio .NET
Using Barcode generation for .NET Control to generate, create bar code image in VS .NET applications.
Create ANSI/AIM Code 39 In .NET Framework
Using Barcode creator for ASP.NET Control to generate, create Code 39 Full ASCII image in ASP.NET applications.
Code 3 Of 9 Generator In Visual C#.NET
Using Barcode generation for VS .NET Control to generate, create Code 3/9 image in .NET applications.
Creating GS1 - 13 In .NET Framework
Using Barcode creation for Visual Studio .NET Control to generate, create EAN / UCC - 13 image in .NET framework applications.