Tutorial by Examples: f

There are a couple of ways to delete a column in a DataFrame. import numpy as np import pandas as pd np.random.seed(0) pd.DataFrame(np.random.randn(5, 6), columns=list('ABCDEF')) print(df) # Output: # A B C D E F # 0 -0.895467 0.386902...

This example assumes you know how to test a Flask app using pytest Below is an API that takes a JSON input with integer values a and b e.g. {"a": 1, "b": 2}, adds them up and returns sum a + b in a JSON response e.g. {"sum": 3}. # hello_add.py from flask import Flask...

Generics are placeholders for types, allowing you to write flexible code that can be applied across multiple types. The advantage of using generics over Any is that they still allow the compiler to enforce strong type-safety. A generic placeholder is defined within angle brackets <>. Generic...

Returns a Boolean indicating if the class conform the protocol: [MyClass conformsToProtocol:@protocol(MyProtocol)];

fs.access() determines whether a path exists and what permissions a user has to the file or directory at that path. fs.access doesn't return a result rather, if it doesn't return an error, the path exists and the user has the desired permissions. The permission modes are available as a property on ...

In $e:expr, the expr is called the fragment specifier. It tells the parser what kind of tokens the parameter $e is expecting. Rust provides a variety of fragment specifiers to, allowing the input to be very flexible. SpecifierDescriptionExamplesidentIdentifierx, foopathQualified namestd::collection...

docker inspect supports Go Templates via the --format option. This allows for better integration in scripts, without resorting to pipes/sed/grep traditional tools. Print a container internal IP: docker inspect --format '{{ .NetworkSettings.IPAddress }}' 7786807d8084 This is useful for direct ne...

Given a sequence of steps we use repeatedly, it's often handy to store it in a function. Pipes allow for saving such functions in a readable format by starting a sequence with a dot as in: . %>% RHS As an example, suppose we have factor dates and want to extract the year: library(magrittr) ...

Suppose we want to write a factory function that accepts an arbitrary list of arguments and passes those arguments unmodified to another function. An example of such a function is make_unique, which is used to safely construct a new instance of T and return a unique_ptr<T> that owns the instan...

If you are building a function that may be heavy on the processor (either clientside or serverside) you may want to consider a memoizer which is a cache of previous function executions and their returned values. This allows you to check if the parameters of a function were passed before. Remember, p...

With virtual member functions: #include <iostream> struct X { virtual void f() { std::cout << "X::f()\n"; } }; struct Y : X { // Specifying virtual again here is optional // because it can be inferred from X::f(). virtual void f() { std::cout <&lt...

A typical use case for a filter is to remove values from an array. In this example we pass in an array and remove any nulls found in it, returning the array. function removeNulls() { return function(list) { for (var i = list.length - 1; i >= 0; i--) { if (typeof list[i...

Another use case for filters is to format a single value. In this example, we pass in a value and we are returned an appropriate true boolean value. function convertToBooleanValue() { return function(input) { if (typeof input !== 'undefined' && input !== null ...

Raw direct IO file_get_contents and file_put_contents provide the ability to read/write from/to a file to/from a PHP string in a single call. file_put_contents can also be used with the FILE_APPEND bitmask flag to append to, instead of truncate and overwrite, the file. It can be used along with LO...

Available in Django 1.9+ from django.contrib.postgres.fields import JSONField from django.db import models class IceCream(models.Model): metadata = JSONField() You can add the normal **options if you wish. ! Note that you must put 'django.contrib.postgres' in INSTALLED_APPS in your s...

Pass data in native Python form, for example list, dict, str, None, bool, etc. IceCream.objects.create(metadata={ 'date': '1/1/2016', 'ordered by': 'Jon Skeet', 'buyer': { 'favorite flavor': 'vanilla', 'known for': ['his rep on SO', 'writing a book'] }, ...

To iterate all files, including in sub directories, use os.walk: import os for root, folders, files in os.walk(root_dir): for filename in files: print root, filename root_dir can be "." to start from current directory, or any other path to start from. Python 3.x3.5 If ...

Using subprocess.Popen give more fine-grained control over launched processes than subprocess.call. Launching a subprocess process = subprocess.Popen([r'C:\path\to\app.exe', 'arg1', '--flag', 'arg']) The signature for Popen is very similar to the call function; however, Popen will return immedi...

The vast majority of Python memory management is handled with reference counting. Every time an object is referenced (e.g. assigned to a variable), its reference count is automatically increased. When it is dereferenced (e.g. variable goes out of scope), its reference count is automatically decreas...

The only time the garbage collector is needed is if you have a reference cycle. The simples example of a reference cycle is one in which A refers to B and B refers to A, while nothing else refers to either A or B. Neither A or B are accessible from anywhere in the program, so they can safely be dest...