You can run into problems with primitives because Python, unlike C, does not let you track (easily) the reference of an object. If I pass in an integer variable, I can't change the value of the variable in its original location, only within the scope of the function. This can be solved with global variables, but only by being very messy. Consider the following code:
def foo(x):
x = 3
myVar = 5
foo(myVar)
print(myVar)You can run into problems with primitives because Python, unlike C, does not let you track (easily) the reference of an object. If I pass in an integer variable, I can't change the value of the variable in its original location, only within the scope of the function. This can be solved with global variables, but only by being very messy. Consider the following code:
def foo(x):
x = 3
myVar = 5
foo(myVar)
print(myVar)This will, of course, output 5, not three. There is no "x*" like there is in C, so solving this would be rather tricky in Python if we wanted foo to reassign 3 to the input variable. Rather, we could write
class Foo:
x = 5
def foo(fooObj):
fooObj.x = 3
myFoo = Foo()
foo(myFoo)
print(myFoo.x)In Python class or object variables are passed to methods explicitly, just as you would do in C if you want to do OOP. This is different from other object oriented languages, like Java or C++, where this argument is passed implicitly (but it always is!). Thus if you define class like:
Class B(object):
def __init__(self,
var = None): # this is constructor
self.var =
var
def func2(self):
print self.varwhen you call object method with . operator, this object will be passed as the first argument, that maps to self in method signature:
b = B(1) # object b is created and B.__init__(b, 1) is called b.func2() # B.func2(b) is called, outputs 1
Last Updated : 22 Apr, 2022
Address of self = 140124194801032
Address of class object = 140124194801032Model is audi a4
color is blue
Model is ferrari 488
color is greenwe have used another parameter name in place of self
Class variable − A variable that is shared by all instances of a class. Class variables are defined within a class but outside any of the class's methods. Class variables are not used as frequently as instance variables are.,The variable empCount is a class variable whose value is shared among all instances of a this class. This can be accessed as Employee.empCount from inside the class or outside the class.,Instance variable − A variable that is defined inside a method and belongs only to the current instance of a class.,Class − A user-defined prototype for an object that defines a set of attributes that characterize any object of the class. The attributes are data members (class variables and instance variables) and methods, accessed via dot notation.
The class statement creates a new class definition. The name of the class immediately follows the keyword class followed by a colon as follows −
class ClassName:
'Optional class documentation string'
class_suiteFollowing is the example of a simple Python class −
class Employee:
'Common base class for all employees'
empCount = 0
def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1
def displayCount(self):
print "Total Employee %d" % Employee.empCount
def displayEmployee(self):
print "Name : ", self.name, ", Salary: ", self.salaryTo create instances of a class, you call the class using class name and pass in whatever arguments its __init__ method accepts.
"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)#!/usr/bin/python
class Employee:
'Common base class for all employees'
empCount = 0
def __init__(self, name, salary):
self.name = name
self.salary = salary
Employee.empCount += 1
def displayCount(self):
print "Total Employee %d" % Employee.empCount
def displayEmployee(self):
print "Name : ", self.name, ", Salary: ", self.salary
"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print "Total Employee %d" % Employee.empCountWhen the above code is executed, it produces the following result −
Name: Zara, Salary: 2000 Name: Manni, Salary: 5000 Total Employee 2
If a function or variable isn’t logically tied to a class, put it at the top level. If you’re worried about name collisions, give it a more precise name or move it to a separate library that can be imported with a prefix.,Local variables, especially in modern code where functions tend to be small, have very little scope. Omitting the type focuses the reader’s attention on the more important name of the variable and its initialized value.,Dart is a “pure” object-oriented language in that all objects are instances of classes. But Dart does not require all code to be defined inside a class—you can define top-level variables, constants, and functions like you can in a procedural or functional language.,The caller cares mostly about the result. If you want the caller to worry about how the operation produces its result more than they do the result being produced, then give the operation a verb name that describes the work and make it a method.
E for the element type in a collection:
class IterableBase<E> {}
class List<E> {}
class HashSet<E> {}
class RedBlackTree<E> {}K and V for the key and value types in an associative
collection:
class Map<K, V> {}
class Multimap<K, V> {}
class MapEntry<K, V> {}R for a type used as the return type of a function or a class’s
methods. This isn’t common, but appears in typedefs sometimes and in classes
that implement the visitor pattern:
abstract class ExpressionVisitor<R> {
R visitBinary(BinaryExpression node);
R visitLiteral(LiteralExpression node);
R visitUnary(UnaryExpression node);
}Otherwise, use T, S, and U for generics that have a single type
parameter and where the surrounding type makes its meaning obvious. There
are multiple letters here to allow nesting without shadowing a surrounding
name. For example:
class Future<T> {
Future<S> then<S>(FutureOr<S> onValue(T value)) => ...
}This does not mean the operation has to be particularly fast in order to
be a getter. IterableBase.length is O(n), and that’s OK. It’s fine for a
getter to do significant calculation. But if it does a surprising amount
of work, you may want to draw their attention to that by making it a method
whose name is a verb describing what it does.
connection.nextIncomingMessage; // Does network I/O.
expression.normalForm; // Could be exponential to calculate.The “user-visible” part is important. It’s fine for getters to modify hidden state or produce out of band side effects. Getters can lazily calculate and store their result, write to a cache, log stuff, etc. As long as the caller doesn’t care about the side effect, it’s probably fine.
stdout.newline; // Produces output.
list.clear; // Modifies object.Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callable parameters, but they have many other uses. , Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from). See the following example: , Closures can also be used as the values of variables; PHP automatically converts such expressions into instances of the Closure internal class. Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon: , Closures may also inherit variables from the parent scope. Any such variables must be passed to the use language construct. As of PHP 7.1, these variables must not include superglobals, $this, or variables with the same name as a parameter. A return type declaration of the function has to be placed after the use clause.
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NULL
string(5)
"hello"
string(5)
"hello"
string(5)
"hello"
string(5)
"world"
string(11)
"hello world"
string(11)
"hello world"object(Test) #1 (0) {
}Notice: Undefined variable: this in % s on line % d
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