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>>> expression = '5 + 3 * a' >>> a = 5 >>> result = eval(expression) >>> result 20

compile built-in function can be used to precompile an expression to a code object; this code object can then be passed to eval. This will speed up the repeated executions of the evaluated code. The 3rd parameter to compile needs to be the string 'eval'. >>> code = compile('a * b + c', '&l...

>>> variables = {'a': 6, 'b': 7} >>> eval('a * b', globals=variables) 42 As a plus, with this the code cannot accidentally refer to the names defined outside: >>> eval('variables') {'a': 6, 'b': 7} >>> eval('variables', globals=variables) Traceback (most ...

You can fetch the current properties of the Annotation by using Reflection to fetch the Method or Field or Class which has an Annotation applied to it, and then fetching the desired properties. @Retention(RetentionPolicy.RUNTIME) @interface MyAnnotation { String key() default "foo";...

As the static keyword is used for accessing fields and methods without an instantiated class, it can be used to declare constants for use in other classes. These variables will remain constant across every instantiation of the class. By convention, static variables are always ALL_CAPS and use unders...

Static gives a method or variable storage that is not allocated for each instance of the class. Rather, the static variable is shared among all class members. Incidentally, trying to treat the static variable like a member of the class instance will result in a warning: public class Apple { pu...

It is possible to create a QtQuick view directly from C++ and to expose to QML C++ defined properties. In the code below the C++ program creates a QtQuick view and exposes to QML the height and width of the view as properties. main.cpp #include <QApplication> #include <QQmlContext> #...

The Application directive defines application-specific attributes. It is provided at the top of the global.aspx file. The basic syntax of Application directive is: <%@ Application Language="C#" %> The attributes of the Application directive are: AttributesDescriptionInheritsThe...

>>> '{0:.0f}'.format(42.12345) '42' >>> '{0:.1f}'.format(42.12345) '42.1' >>> '{0:.3f}'.format(42.12345) '42.123' >>> '{0:.5f}'.format(42.12345) '42.12345' >>> '{0:.7f}'.format(42.12345) '42.1234500' Same hold for other way of referenc...

Using threading & queue: from socket import socket, AF_INET, SOCK_STREAM from threading import Thread from queue import Queue def echo_server(addr, nworkers): print('Echo server running at', addr) # Launch the client workers q = Queue() for n in range(nworkers): ...

Differences in subsetting syntax A data.table is one of several two-dimensional data structures available in R, besides data.frame, matrix and (2D) array. All of these classes use a very similar but not identical syntax for subsetting, the A[rows, cols] schema. Consider the following data stored i...

Delegates may have variant type parameters. delegate void Action<in T>(T t); // T is an input delegate T Func<out T>(); // T is an output delegate T2 Func<in T1, out T2>(); // T1 is an input, T2 is an output This follows from the Liskov Substitution Principle, w...

Category theory is a modern mathematical theory and a branch of abstract algebra focused on the nature of connectedness and relation. It is useful for giving solid foundations and common language to many highly reusable programming abstractions. Haskell uses Category theory as inspiration for some o...

A category C consists of: A collection of objects called Obj(C) ; A collection (called Hom(C)) of morphisms between those objects. If a and b are in Obj(C), then a morphism f in Hom(C) is typically denoted f : a -> b, and the collection of all morphism between a and b is denoted hom(a,b) ; A...

If you have a string that contains Python literals, such as strings, floats etc, you can use ast.literal_eval to evaluate its value instead of eval. This has the added feature of allowing only certain syntax. >>> import ast >>> code = """(1, 2, {'foo': 'bar'})&quot...

Detailed instructions on getting forms set up or installed.

First of all, you cannot "install" Java EE. Java EE consists of a number of specifications. You can install implementations of those specifications however. Depending on your needs, there are lots of possibilities. To install most (or all) of the specifications, you can choose a Java EE...

<div class="navbar navbar-inverse navbar-fixed-top"> <div class="container"> <div class="navbar-header"> <!--- vvv Hamburger icon that gets shown when window reaches a certain scale vvv ---> <button type...

using System; using System.Web; using System.Web.Mvc; namespace Example.SDK.Filters { [AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = false)] public sealed class CustomErrorHandlerFilter : HandleErrorAttribute { public override void OnExceptio...

You can choose between major distributions of LaTeX: TeX Live (Windows, Linux, and OS X), the standard, cross-platform distribution. MacTeX (Mac) A packaged version of TeX Live made for OS X with some Mac-specific tools MiKTeX (Windows) A separate distribution entirely that All distributions...