Reflection/List properties: Difference between revisions
creation: JavaScript, Python |
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Some languages support dynamic properties, which in general can only be inspected if a class' public API includes a way of listing them. |
Some languages support dynamic properties, which in general can only be inspected if a class' public API includes a way of listing them. |
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=={{header|Java}}== |
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<lang java>import java.lang.reflect.Field; |
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public class ListFields { |
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public int examplePublicField; |
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private boolean examplePrivateField; |
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public static void main(String[] args) { |
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Class clazz = ListFields.class; |
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System.out.println("All public fields (including inherited):"); |
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for (Field f : clazz.getFields()) { |
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System.out.println(f); |
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} |
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System.out.println(); |
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System.out.println("All declared fields (excluding inherited):"); |
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for (Field f : clazz.getDeclaredFields()) { |
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System.out.println(f); |
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} |
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} |
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}</lang> |
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{{out}} |
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<pre> |
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All public fields (including inherited): |
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public int ListFields.examplePublicField |
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All declared fields (excluding inherited): |
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public int ListFields.examplePublicField |
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private boolean ListFields.examplePrivateField |
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</pre> |
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=={{header|JavaScript}}== |
=={{header|JavaScript}}== |
Revision as of 19:09, 6 August 2016
You are encouraged to solve this task according to the task description, using any language you may know.
- Task
The goal is to get the properties of an object, as names, values or both.
Some languages support dynamic properties, which in general can only be inspected if a class' public API includes a way of listing them.
Java
<lang java>import java.lang.reflect.Field;
public class ListFields {
public int examplePublicField; private boolean examplePrivateField; public static void main(String[] args) { Class clazz = ListFields.class;
System.out.println("All public fields (including inherited):"); for (Field f : clazz.getFields()) { System.out.println(f); } System.out.println(); System.out.println("All declared fields (excluding inherited):"); for (Field f : clazz.getDeclaredFields()) { System.out.println(f); } }
}</lang>
- Output:
All public fields (including inherited): public int ListFields.examplePublicField All declared fields (excluding inherited): public int ListFields.examplePublicField private boolean ListFields.examplePrivateField
JavaScript
There are multiple ways of getting property names, each of which include different subsets of an object's properties, such as enumerable or inherited properties. Properties in JavaScript can be enumerable or non-enumerable; enumerable properties are accessable when looping over the object with for
. Object.getOwnPropertyNames()
.
<lang javascript>var obj = Object.create({
name: 'proto', proto: true, doNothing: function() {} }, { name: {value: 'obj', writable: true, configurable: true, enumerable: true}, obj: {value: true, writable: true, configurable: true, enumerable: true}, 'non-enum': {value: 'non-enumerable', writable: true, enumerable: false}, doStuff: {value: function() {}, enumerable: true}
});
// get enumerable properties on an object and its ancestors function get_property_names(obj) {
var properties = []; for (var p in obj) { properties.push(p); } return properties;
}
get_property_names(obj); //["name", "obj", "doStuff", "proto", "doNothing"]
Object.getOwnPropertyNames(obj); //["name", "obj", "non-enum", "doStuff"]
Object.keys(obj); //["name", "obj", "doStuff"]
Object.entries(obj); //[["name", "obj"], ["obj", true], ["doStuff", function()]] </lang>
Python
The dir()
function and Python's inspect
module both will list properties.
<lang python>class Parent(object):
__priv = 'private' def __init__(self, name): self.name = name def __repr__(self): return '%s(%s)' % (type(self).__name__, self.name) def doNothing(self): pass
import re
class Child(Parent):
# prefix for "private" fields __rePrivate = re.compile('^_(Child|Parent)__') # used when setting dynamic property values __reBleh = re.compile('\Wbleh$') @property def reBleh(self): return self.__reBleh def __init__(self, name, *args): super(Child, self).__init__(name) self.args = args def __dir__(self): myDir = filter( # filter out private fields lambda p: not self.__rePrivate.match(p), list(set( \ sum([dir(base) for base in type(self).__bases__], []) \ + type(self).__dict__.keys() \ + self.__dict__.keys() \ ))) return myDir + map( # dynamic properties lambda p: p + '_bleh', filter( # don't add dynamic properties for methods and other special properties lambda p: (p[:2] != '__' or p[-2:] != '__') and not callable(getattr(self, p)), myDir)) def __getattr__(self, name): if name[-5:] == '_bleh': # dynamic '_bleh' properties return str(getattr(self, name[:-5])) + ' bleh' if hasattr(super(Child, chld), '__getattr__'): return super(Child, self).__getattr__(name) raise AttributeError("'%s' object has no attribute '%s'" % (type(self).__name__, name)) def __setattr__(self, name, value): if name[-5:] == '_bleh': # skip backing properties that are methods if not (hasattr(self, name[:-5]) and callable(getattr(self, name[:-5]))): setattr(self, name[:-5], self.reBleh.sub(, value)) elif hasattr(super(Child, self), '__setattr__'): super(Child, self).__setattr__(name, value) elif hasattr(self, '__dict__'): self.__dict__[name] = value def __repr__(self): return '%s(%s, %s)' % (type(self).__name__, self.name, str(self.args).strip('[]()')) def doStuff(self): return (1+1.0/1e6) ** 1e6
par = Parent('par') par.parent = True dir(par)
- ['_Parent__priv', '__class__', ..., 'doNothing', 'name', 'parent']
inspect.getmembers(par)
- [('_Parent__priv', 'private'), ('__class__', <class '__main__.Parent'>), ..., ('doNothing', <bound method Parent.doNothing of <__main__.Parent object at 0x100777650>>), ('name', 'par'), ('parent', True)]
chld = Child('chld', 0, 'I', 'two') chld.own = "chld's own" dir(chld)
- ['__class__', ..., 'args', 'args_bleh', 'doNothing', 'doStuff', 'name', 'name_bleh', 'own', 'own_bleh', 'reBleh', 'reBleh_bleh']
inspect.getmembers(chld)
- [('__class__', <class '__main__.Child'>), ..., ('args', (0, 'I', 'two')), ('args_bleh', "(0, 'I', 'two') bleh"), ('doNothing', <bound method Child.doNothing of Child(chld, 0, 'I', 'two')>), ('doStuff', <bound method Child.doStuff of Child(chld, 0, 'I', 'two')>), ('name', 'chld'), ('name_bleh', 'chld bleh'), ('own', "chld's own"), ('own_bleh', "chld's own bleh"), ('reBleh', <_sre.SRE_Pattern object at 0x10067bd20>), ('reBleh_bleh', '<_sre.SRE_Pattern object at 0x10067bd20> bleh')]
</lang>