Tutorial by Examples: p

The Python Standard Library includes an interactive debugging library called pdb. pdb has extensive capabilities, the most commonly used being the ability to 'step-through' a program. To immediately enter into step-through debugging use: python -m pdb <my_file.py> This will start the debu...

PHP 7 introduces a new kind of operator, which can be used to compare expressions. This operator will return -1, 0 or 1 if the first expression is less than, equal to, or greater than the second expression. // Integers print (1 <=> 1); // 0 print (1 <=> 2); // -1 print (2 <=> 1...

setTimeout Executes a function, after waiting a specified number of milliseconds. used to delay the execution of a function. Syntax : setTimeout(function, milliseconds) or window.setTimeout(function, milliseconds) Example : This example outputs "hello" to the console after 1 secon...

Responses can be written to a http.ResponseWriter using templates in Go. This proves as a handy tool if you wish to create dynamic pages. (To learn how Templates work in Go, please visit the Go Templates Documentation page.) Continuing with a simple example to utilise the html/template to respond ...

Normal types, like String, are not nullable. To make them able to hold null values, you have to explicitly denote that by putting a ? behind them: String? var string : String = "Hello World!" var nullableString: String? = null string = nullableString // Compiler error: Can't...

To access functions and properties of nullable types, you have to use special operators. The first one, ?., gives you the property or function you're trying to access, or it gives you null if the object is null: val string: String? = "Hello World!" print(string.length) // Compile erro...

In order to install PostgreSQL on OSX, you need to know which versions are currently supported. Use this command to see what versions you have available. sudo port list | grep "^postgresql[[:digit:]]\{2\}[[:space:]]" You should get a list that looks something like the following: post...

If need set value 0 to column B, where in column A are duplicated data first create mask by Series.duplicated and then use DataFrame.ix or Series.mask: In [224]: df = pd.DataFrame({'A':[1,2,3,3,2], ...: 'B':[1,7,3,0,8]}) In [225]: mask = df.A.duplicated(keep=False) In...

Use drop_duplicates: In [216]: df = pd.DataFrame({'A':[1,2,3,3,2], ...: 'B':[1,7,3,0,8]}) In [217]: df Out[217]: A B 0 1 1 1 2 7 2 3 3 3 3 0 4 2 8 # keep only the last value In [218]: df.drop_duplicates(subset=['A'], keep='last') Out[218]: ...

The unary plus (+) precedes its operand and evaluates to its operand. It attempts to convert the operand to a number, if it isn't already. Syntax: +expression Returns: a Number. Description The unary plus (+) operator is the fastest (and preferred) method of converting something into a n...

The delete operator deletes a property from an object. Syntax: delete object.property delete object['property'] Returns: If deletion is successful, or the property did not exist: true If the property to be deleted is an own non-configurable property (can't be deleted): false in non...

The typeof operator returns the data type of the unevaluated operand as a string. Syntax: typeof operand Returns: These are the possible return values from typeof: TypeReturn valueUndefined"undefined"Null"object"Boolean"boolean"Number"number"String&quot...

The void operator evaluates the given expression and then returns undefined. Syntax: void expression Returns: undefined Description The void operator is often used to obtain the undefined primitive value, by means of writing void 0 or void(0). Note that void is an operator, not a functio...

The unary negation (-) precedes its operand and negates it, after trying to convert it to number. Syntax: -expression Returns: a Number. Description The unary negation (-) can convert the same types / values as the unary plus (+) operator can. Values that can't be converted will evaluat...

The bitwise NOT (~) performs a NOT operation on each bit in a value. Syntax: ~expression Returns: a Number. Description The truth table for the NOT operation is: aNOT a01101337 (base 10) = 0000010100111001 (base 2) ~1337 (base 10) = 1111101011000110 (base 2) = -1338 (base 10) A bit...

The logical NOT (!) operator performs logical negation on an expression. Syntax: !expression Returns: a Boolean. Description The logical NOT (!) operator performs logical negation on an expression. Boolean values simply get inverted: !true === false and !false === true. Non-boolean val...

DynamoDB is a fully managed service provided by AWS. It does not need to be installed or configured. AWS is responsible for all administrative burdens of operating, scalling and backup/restore of the distributed database.

It's often useful to combine multiple plot types in one graph (for example a Barplot next to a Scatterplot.) R makes this easy with the help of the functions par() and layout(). par() par uses the arguments mfrow or mfcol to create a matrix of nrows and ncols c(nrows, ncols) which will serve as a ...

All DATEs have a time component; however, it is customary to store dates which do not need to include time information with the hours/minutes/seconds set to zero (i.e. midnight). Use an ANSI DATE literal (using ISO 8601 Date format): SELECT DATE '2000-01-01' FROM DUAL; Convert it from a string ...

Convert it from a string literal using TO_DATE(): SELECT TO_DATE( '2000-01-01 12:00:00', 'YYYY-MM-DD HH24:MI:SS' ) FROM DUAL; Or use a TIMESTAMP literal: CREATE TABLE date_table( date_value DATE ); INSERT INTO date_table ( date_value ) VALUES ( TIMESTAMP '2000-01-01 12:00:00' ); Oracl...