python empty string

1. null The null keyword is a text value that does not reference any object's null reference. Null is the default value of the reference type variable. Then, only the referenced variable can be null. If int I = NULL, it is not possible because Int Is of the value type. 2., "" And string. Empty Both are empty strings. But "" theoretically re-opens the memory sp

that it is a null value, but for ordinary users, undefined is very confusing, how can we in a shape field is empty, Replace with an empty string? With IsNull must not be solved, do not worry, we can use IsNull, case when and conver function to solve. 2. Case Two formats for case 1. Simple Case function case sex when " 1 then male

used to determine the reference invalidate. 3. "And string. Empty Both of these are empty strings, with a focus on the difference between string str1 = "" and string str2 = NULL. After this definition, str1 is an empty

Can write a nssring category to add some methods to NSString, and these methods are some regular expressions.Like writing a class called Helper, it's nsstring+helper.The. h and. m files are then written.#pragma mark-Verify related/* Verify related *///1. Is the mobile number- (BOOL) ISMOBILENUMBER;//2. Is the mailbox-(BOOL) ISVALIDATEEMAIL;//3. Whether it is an empty string- (BOOL) ISNULLSTR;//4. Whether i

Let's look at an effect chart first. When you define only one str instead of allocating memory for it, use string str=null, but you must assign a value to it before you use it, such as str= "XXXX", which is initialized for it.and string str= string. Empty is defined and initialized together it is actually equivalent

empty string "" 1, type:"" is an empty string (String), the length of 0, accounting for memory , in memory allocated a space , you can use object The method in. (For example: "". toString (), etc.) 2. Memory allocation: Declares a reference to a

database. Why does it indicate the reason for the classes (such as datarow) That DOTNET stores the data) all store data in the form of objects. For datarow, the value returned by its row [column] is never null, or it is a specific value of the column type. Or dbnull. Therefore, the row [column]. tostring () Statement will never cause nullreferenceexception in tostring. Dbnull implements iconvertible. However, except that tostring is normal, other toxxx will throw an error that cannot be convert

Null is a C # keyword and is a literal value that represents a null reference that does not reference any object. NULL is the default value for reference to a type variable. Then only the reference variable can be null, and if int i=null, it is not possible, because int is a value type. String. Empty is the equivalent of "", but they and Null are two different things. It is said to be:

/*** Function: There is an array of sorted strings, which scatter some empty strings to find the position of the given string. *//** * Idea: Make changes to the binary lookup method, and, if mid is an empty string, swap the mid to the position of the non-empty

Determine the relationship between 0 and ', null, empty, False $a = 0; The relationship between echo "0 and", empty, NULL, false: "; if ($a = = ") { echo "0 = ="; "; }else{ echo "0! ="; "; } if (trim ($a) = = ") { echo "Trim (0) = ="; "; }else{ echo "Trim (0)! ="; "; } if (strval ($a) = = ") { echo "Strval (0) = ="; "; }else{ echo "Strval (0)! ="; "; } if ($a = = =) { echo "0 = = ="; "; }else{ echo "0!=== '

1 to construct a long string, you can create an empty string as the initial value. You can assign an empty string literal to a variable, or you can initialize a new string instance:2var emptystring ="" //

Encountered a strange problem in a project that cost me a lot of time without solving final debugging discovery is the question of judgment--about 0 and ' (empty single quotes, for good see I add a space) judgment, I found 0== "incredibly set up, depressed at the same time decided to write a simple page test, vowed to 0,null , empty, empty, false relationships ar

In the actual development project, the server often uses the empty string "" as the return result to represent the null value, but this will encounter the problem in the Gson, if this data type is not the string, Gson parsing will be an errorWe want the program to automatically parse an empty

MySQL table structure where the fields my_dateDateTime DEFAULT NULL, See a simple Insert code first $sql = "INSERT into My_test (my_date) VALUES (')"; Mysqli_query ($DBC, $sql); Insert failed How do I insert an empty string into mysql datetime or int? Of course I also know $sql = "INSERT into My_test (my_date) VALUES (null)"; can be inserted successfully;But the insert code is that my backup database (. sq

In JavaScript, we are often exposed to the 5 more special objects mentioned in the topic--false, 0, empty strings, null, and undefined. These objects are easy to use, so you have to be careful when you use them.Type detectionLet's come down and see what their type is:　　Running the above code, the dialog box that pops up should display true. That is, False is a Boolean type object, 0 is a numeric type object, an em