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A method defined in an interface is by default public abstract. When an abstract class implements an interface, any methods which are defined in the interface do not have to be implemented by the abstract class. This is because a class that is declared abstract can contain abstract method declaratio...

var a:Object; trace(a); // null trace(a.b); // Error 1009 Here, an object reference is declared, but is never assigned a value, be it with new or assignment of a non-null value. Requesting its properties or method results in a 1009 error.

interface ITable { // an indexer can be declared in an interface object this[int x, int y] { get; set; } } class DataTable : ITable { private object[,] cells = new object[10, 10]; /// <summary> /// implementation of the indexer declared in the interface //...

To destroy, delete, or unset an array: unset array To destroy, delete, or unset a single array element: unset array[10]

This validation restricts the insertion of only numeric values. class Player < ApplicationRecord validates :points, numericality: true validates :games_played, numericality: { only_integer: true } end Besides :only_integer, this helper also accepts the following options to add constrai...

This helper validates that the attribute's value is unique right before the object gets saved. class Account < ApplicationRecord validates :email, uniqueness: true end There is a :scope option that you can use to specify one or more attributes that are used to limit the uniqueness check: ...

This helper validates that the specified attributes are not empty. class Person < ApplicationRecord validates :name, presence: true end Person.create(name: "John").valid? # => true Person.create(name: nil).valid? # => false You can use the absence helper to validate th...

class Person < ApplicationRecord validates :name, length: { minimum: 2 } validates :bio, length: { maximum: 500 } validates :password, length: { in: 6..20 } validates :registration_number, length: { is: 6 } end The possible length constraint options are: :minimum - The attribut...

Unlike Big-O notation, which represents only upper bound of the running time for some algorithm, Big-Theta is a tight bound; both upper and lower bound. Tight bound is more precise, but also more difficult to compute. The Big-Theta notation is symmetric: f(x) = Ө(g(x)) <=> g(x) = Ө(f(x)) An ...

Overload resolution occurs after name lookup. This means that a better-matching function will not be selected by overload resolution if it loses name lookup: void f(int x); struct S { void f(double x); void g() { f(42); } // calls S::f because global f is not visible here, ...

Boolean logic expressions, in addition to evaluating to True or False, return the value that was interpreted as True or False. It is Pythonic way to represent logic that might otherwise require an if-else test. And operator The and operator evaluates all expressions and returns the last expressi...

Number of unique elements in a series: In [1]: id_numbers = pd.Series([111, 112, 112, 114, 115, 118, 114, 118, 112]) In [2]: id_numbers.nunique() Out[2]: 5 Get unique elements in a series: In [3]: id_numbers.unique() Out[3]: array([111, 112, 114, 115, 118], dtype=int64) In [4]: df = pd.Da...

class File(): def __init__(self, filename, mode): self.filename = filename self.mode = mode def __enter__(self): self.open_file = open(self.filename, self.mode) return self.open_file def __exit__(self, *args): self.open_file.close() ...

You need to set who you are *before* creating any commit. That will allow commits to have the right author name and email associated to them. It has nothing to do with authentication when pushing to a remote repository (e.g. when pushing to a remote repository using your GitHub, BitBucket, or Gi...

Swallowing Exceptions One should always re-throw exception in the following way: try { ... } catch (Exception ex) { ... throw; } Re-throwing an exception like below will obfuscate the original exception and will lose the original stack trace. One should never do this! The st...

You can get list of available commands by following way: >>> python manage.py help If you don't understand any command or looking for optional arguments then you can use -h argument like this >>> python manage.py command_name -h Here command_name will be your desire command...

CSV(Comma Separated Values) is a simple file format used to store tabular data, such as a spreadsheet. This is a minimal example of how to write & read data in Python. Writing data to a CSV file: import csv data = [["Ravi", "9", "550"], ["Joe", "8...

Example for continue for i in [series] do command 1 command 2 if (condition) # Condition to jump over command 3 continue # skip to the next value in "series" fi command 3 done Example for break for i in [series] do command 4 if (condi...

Pass an open file object from Python to C extension code. You can convert the file to an integer file descriptor using PyObject_AsFileDescriptor function: PyObject *fobj; int fd = PyObject_AsFileDescriptor(fobj); if (fd < 0){ return NULL; } To convert an integer file descriptor back ...

if true do "Will be seen since condition is true." end if false do "Won't be seen since condition is false." else "Will be seen. end unless false do "Will be seen." end unless true do "Won't be seen." else ...