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Python Articles
Page 854 of 855
What are repeating character classes used in Python regular expression?
A character class followed by operators like '?', '*' or '+' are called repeating character classes.If you repeat a character class by using the '?', '*' or '+' operators, you will repeat the entire character class, and not just the character that it matched. The regex '[0-9]+' can match '579' as well as '333'. If you want to repeat the matched character, rather than the class, you will need to use backreferences. '([0- 9])\1+' will match '333' but not “579”. When applied to the string “922226”, it will match '2222' in the middle of this string. If you do not ...
Read MoreWhat is the difference between __str__ and __repr__ in Python?
The built-in functions repr() and str() respectively call object.__repr__(self) and object.__str__(self) methods. First function computes official representation of the object, while second returns informal representation of the object. Result of both functions is same for integer object. >>> x = 1 >>> repr(x) '1' >>> str(x) '1' However, it is not the case for string object. >>> x = "Hello" >>> repr(x) "'Hello'" >>> str(x) 'Hello' Return value of repr() of a string object can be evaluated by eval() function and results in valid string object. However, result of str() can not be evaluated. ...
Read MoreHow many Python classes should I put in one file?
Python code is organized in files called "modules" and groups of related modules called “packages".A module is a distinct unit that may have one or more closely-related classes. Modules need to be imported before they are read, used, maintained and extended if needed. So a module is a unit or reuse.The rule is this: a module is the unit of reuse. Everything in Python libraries and other Python applications is either a module or a package of modules.There is no limit on how many classes one can put in a file or a module. It all depends on how big ...
Read MoreHow do you compare Python objects with .NET objects?
By default, all .NET objects are reference types and their equality and hash code is determined by their memory address. Additionally, assigning a variable to an existing object just makes it point to that address in memory, so there is no costly copying occurring. It appears that this is true for python objects as well to certain extent.Properties of Python objects: All python objects havea unique identity (an integer, returned by id(x)); a type (returned by type(x))You cannot change the identity; You cannot change the type.Some objects allow you to change their content (without changing the identity or the type, that is).Some ...
Read MoreHow to compress Python objects before saving to cache?
We need sometimes to compress Python objects (list, dictionary, string, etc) before saving them to cache and decompress after reading from cache.Firstly we need to be sure we need to compress the objects. We should check if the data structures/objects are too big just to fit uncompressed in the cache. There is going to be an overhead for compression/decompression, that we have to tradeoff with the gains made by caching in the first place.If we really need compression, then we probably want to use zlib.If we are going to use zlib, we might want to experiment with the different compression ...
Read MoreHow do cookies work in Python CGI Programming?
Using Cookies in CGIHTTP protocol is a stateless protocol. For a commercial website, it is required to maintain session information among different pages. For example, one user registration ends after completing many pages. How to maintain user's session information across all the web pages?In many situations, using cookies is the most efficient method of remembering and tracking preferences, purchases, commissions, and other information required for better visitor experience or site statistics.How Cookies workYour server sends some data to the visitor's browser in the form of a cookie. The browser may accept the cookie. If it does, it is stored as ...
Read MoreWhen are python objects candidates for garbage collection?
A python object or variable will be eligible for garbage collection as soon as all references to it go out of scope or are manually deleted (del x). We would have to presume there were no references to the object anywhere else for it to be garbage collected.
Read MoreHow to exit from a Python if clause?
It is not possible to exit from an if block of Python code. The break keyword does appear in if block but it has to inside a loop. It is however possible to exit from entire program from inside if block by sys.exit()
Read MoreWhat is the difference between the != and <> operators in Python?
In Python 2.x, both != and operators are available to check if two operands are not equal. Both return true if operands are not equal and false if they are equal.In Python 3.x, operator has been deprecated.
Read MoreWhy there is not do...while loop in Python?
PEP 315 (Python Enhancement Proposal) to include do..while statement has been rejected because it doen't fit in the general format of indented block statement: indented block used by every other Python compound statement. In words of Guido Van Rossum - "Please reject the PEP. More variations along these lines won't make the language more elegant or easier to learn. They'd just save a few hasty folks some typing while making others who have to read/maintain their code wonder what it means".
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