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Python Articles
Page 809 of 855
How to replace values of a Python dictionary?
You can assign a dictionary value to a variable in Python using the access operator []. For example,Examplemy_dict = { 'foo': 42, 'bar': 12.5 } new_var = my_dict['foo'] print(new_var)OutputThis will give the output −42This syntax can also be used to reassign the value associated with this key. For example,Examplemy_dict = { 'foo': 42, 'bar': 12.5 } my_dict['foo'] = "Hello" print(my_dict['foo'])OutputThis will give the output −Hello
Read MoreHow to deploy python modules on Heroku?
Assuming you have set up Python 3.6, Pipenv and heroku CLI installed locally and are logged in on Heroku from the CLI using the steps mentioned here: https://devcenter.heroku.com/articles/getting-started-with-python#set-up.Your application needs to have a git repository to be deployed to heroku. You need to cd in the directory where the root of your git repo code resides. Now you need to create a heroku application using:$ heroku create Creating lit-bastion-5032 in organization heroku... done, stack is cedar-14https://lit-bastion-5032.herokuapp.com/ | https://git.heroku.com/lit-bastion-5032.gitGit remote heroku addedWhen you create an app, a git remote (called heroku) is also created and associated with your local git repository. ...
Read MoreHow do I format a string using a dictionary in Python 3?
You can use dictionaries to interpolate strings. They have a syntax in which you need to provide the key in the parentheses between the % and the conversion character. For example, if you have a float stored in a key 'cost' and want to format it as '$xxxx.xx', then you'll place '$%(cost).2f' at the place you want to display it.Here is an example of using string formatting in dictionaries to interpolate a string and format a number:>>>print('%(language)s has %(number)03d quote types.' % {'language': "Python", "number": 2}) Python has 002 quote types.You can read up more about string formatting and their ...
Read MoreHow does garbage collection work in Python?
Python deletes unwanted objects (built-in types or class instances) automatically to free the memory space. The process by which Python periodically frees and reclaims blocks of memory that no longer are in use is called Garbage Collection.Python's garbage collector runs during program execution and is triggered when an object's reference count reaches zero. An object's reference count changes as the number of aliases that point to it changes.An object's reference count increases when it is assigned a new name or placed in a container (list, tuple, or dictionary). The object's reference count decreases when it's deleted with del, its reference is ...
Read MoreExplain the variables inside and outside of a class __init__() function in Python.
Class variables vs Instance VariablesAll variables outside the class __init__ function in Python are class variables while those inside the same are instance variables. The difference between the class variables and instance variables is understood better by examining the code belowExampleclass MyClass: stat_elem = 456 def __init__(self): self.object_elem = 789 c1 = MyClass() c2 = MyClass() # Initial values of both elements >>> print c1.stat_elem, c1.object_elem 456 789 >>> print c2.stat_elem, c2.object_elem 456 789 # Let's try changing the static element MyClass.static_elem = 888 ...
Read MoreWhat is difference between self and __init__ methods in python Class?
selfThe word 'self' is used to represent the instance of a class. By using the "self" keyword we access the attributes and methods of the class in python.__init__ method"__init__" is a reseved method in python classes. It is called as a constructor in object oriented terminology. This method is called when an object is created from a class and it allows the class to initialize the attributes of the class.ExampleFind out the cost of a rectangular field with breadth(b=120), length(l=160). It costs x (2000) rupees per 1 square unitclass Rectangle: def __init__(self, length, breadth, unit_cost=0): self.length ...
Read MoreHow to create instance Objects using __init__ in Python?
The instantiation or calling-a-class-object operation creates an empty object. Many classes like to create objects with instances with a specific initial state. Therefore a class may define a special method named __init__(), as follows −def __init__(self) − self.data = [ ]When a class defines an __init__() method, class instantiation automatically invokes the newly-created class instance which is obtained by −x = MyClass()The __init__() method may have arguments. In such a case, arguments given to the class instantiation operator are passed on to __init__(). For example, >>> class Complex: ... def __init__(self, realpart, imagpart): ...
Read MoreHow do you validate a URL with a regular expression in Python?
There's no validate method as almost anything is a valid URL. There are some punctuation rules for splitting it up. Without any punctuation, you still have a valid URL.Depending on the situation, we use following methods.If you trust the data, and just want to verify if the protocol is HTTP, then urlparse is perfect.If you want to make the URL is actually a true URL, use the cumbersome and maniacal regexIf you want to make sure it's a real web address, use the following codeExampleimport urllib try: urllib.urlopen(url) except IOError: print "Not a real URL"
Read MoreHow to use special characters in Python Regular Expression?
From Python documentationNon-special characters match themselves. Special characters don't match themselves −\ Escape special char or start a sequence..Match any char except newline, see re.DOTALL^Match start of the string, see re.MULTILINE $ Match end of the string, see re.MULTILINE[ ]Enclose a set of matchable charsR|S Match either regex R or regex S.()Create capture group, & indicate precedenceAfter '[', enclose a set, the only special chars are −]End the set, if not the 1st char-A range, eg. a-c matches a, b or c^Negate the set only if it is the 1st char Quantifiers (append '?' for non-greedy) ...
Read MoreWhat does "?:" mean in a Python regular expression?
Non capturing groupsIf we do not want a group to capture its match, we can write this regular expression as Set(?:Value). The question mark and the colon after the opening parenthesis are the syntax that creates a non-capturing group. The regex Set(Value)? matches Set or SetValue. In the first case, the first (and only) capturing group remains empty. In the second case, the first capturing group matches Value. The question mark appearing at the end is the quantifier that makes the previous token optional. Set(?:Value) matches Setxxxxx, i.e., all those strings starting with Set but not followed by Value. Such would be ...
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