What's the difference between __builtin__ and __builtins__?
Question:
I was coding today and noticed something. If I open a new interpreter session (IDLE) and check what’s defined with the dir function I get this:
$ python
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']
>>> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs', 'all', 'any', 'apply', 'basestring', 'bin', 'bool', 'buffer', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'cmp', 'coerce', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'execfile', 'exit', 'file', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'intern', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'long', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']
>>> import __builtin__
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs', 'all', 'any', 'apply', 'basestring', 'bin', 'bool', 'buffer', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'cmp', 'coerce', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'execfile', 'exit', 'file', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'intern', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'long', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']
>>> dir(__builtin__) == dir(__builtins__) # They seem to have the same things
True
Please note the last line.
So, my question is:
-
Is any an alias of the other one?
-
Are the Python guys planning to get rid of one of those?
-
What should I use for my own programs?
-
What about Python 3?
-
Any information is valuable!
Important:
I’m using Python 2.7.2+ on Ubuntu.
Answers:
__builtin__ is a module containing the built-in functions and types. The fact that a name __builtins__ is available containing the same things is an implementation detail. In other words, if you need to use one of them, do import __builtin__ and then use __builtin__. See the documentation.
Straight from the python documentation:
http://docs.python.org/reference/executionmodel.html
By default, when in the __main__ module, __builtins__ is the
built-in module __builtin__ (note: no ‘s’); when in any other
module, __builtins__ is an alias for the dictionary of the
__builtin__ module itself.
__builtins__ can be set to a user-created dictionary to create a
weak form of restricted execution.
CPython implementation detail: Users should not touch __builtins__; it is strictly an implementation detail. Users
wanting to override values in the builtins namespace should import
the __builtin__ (no ‘s’) module and modify its attributes
appropriately. The namespace for a module is automatically created the
first time a module is imported.
Note that in Python3, the module __builtin__ has been renamed to builtins to avoid some of this confusion.
You should use __builtin__ in your programs (in the rare cases that you need it), because __builtins__ is an implementation detail of CPython. It may either be identical to __builtin__, or to __builtin__.__dict__, depending on the context. As the documentation says:
Most modules have the name __builtins__ (note the ‘s’) made available as part of their globals. The value of __builtins__ is normally either this module or the value of this modules’s __dict__ attribute. Since this is an implementation detail, it may not be used by alternate implementations of Python.
In Python 3, __builtin__ has been renamed to builtins, and __builtins__ remains the same (so you should only use builtins in Python 3).
Guido wanted to unite __builtin__ and __builtins__, as you can see here (“Having __builtins__ and __builtin__ both is clearly a bad idea.”) , but apparently nothing came of it.
Apparently the use of __builtins__ is for performance – it gives direct access to __builtin__.__dict__ when used in a non-main module, and therefore removes one level of indirection.
You can understand these like following code.
when cpython is started, cpython load __builtin__ modules into global namespace
import __builtin__as __builtins__
The __builtins__ module should not be confused with the __builtin__ module. The
names, of course, are so similar that it tends to lead to some confusion among new Python
programmers who have gotten this far.
The __builtins__ module consists of a set of builtin names for the built-ins namespace. Most, if not all, of these names come from the
__builtin__ module, which is a module of the built-in functions, exceptions, and other
attributes.
In standard Python execution, __builtins__ contains all the names from
__builtin__. Python used to have a restricted execution model that allowed modification of __builtins__ where key pieces from __builtin__ were left out to create a sandbox environment.
However, due its security flaws and the difficulty involved with repairing it,
restricted execution is no longer supported in Python (as of 2.3).
I was coding today and noticed something. If I open a new interpreter session (IDLE) and check what’s defined with the dir function I get this:
$ python
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__']
>>> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs', 'all', 'any', 'apply', 'basestring', 'bin', 'bool', 'buffer', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'cmp', 'coerce', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'execfile', 'exit', 'file', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'intern', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'long', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']
>>> import __builtin__
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BufferError', 'BytesWarning', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', 'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs', 'all', 'any', 'apply', 'basestring', 'bin', 'bool', 'buffer', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'cmp', 'coerce', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'execfile', 'exit', 'file', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'intern', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'long', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip']
>>> dir(__builtin__) == dir(__builtins__) # They seem to have the same things
True
Please note the last line.
So, my question is:
-
Is any an alias of the other one?
-
Are the Python guys planning to get rid of one of those?
-
What should I use for my own programs?
-
What about Python 3?
-
Any information is valuable!
Important:
I’m using Python 2.7.2+ on Ubuntu.
__builtin__ is a module containing the built-in functions and types. The fact that a name __builtins__ is available containing the same things is an implementation detail. In other words, if you need to use one of them, do import __builtin__ and then use __builtin__. See the documentation.
Straight from the python documentation:
http://docs.python.org/reference/executionmodel.html
By default, when in the
__main__module,__builtins__is the
built-in module__builtin__(note: no ‘s’); when in any other
module,__builtins__is an alias for the dictionary of the
__builtin__module itself.
__builtins__can be set to a user-created dictionary to create a
weak form of restricted execution.CPython implementation detail: Users should not touch
__builtins__; it is strictly an implementation detail. Users
wanting to override values in the builtins namespace shouldimport
the__builtin__(no ‘s’) module and modify its attributes
appropriately. The namespace for a module is automatically created the
first time a module is imported.
Note that in Python3, the module __builtin__ has been renamed to builtins to avoid some of this confusion.
You should use __builtin__ in your programs (in the rare cases that you need it), because __builtins__ is an implementation detail of CPython. It may either be identical to __builtin__, or to __builtin__.__dict__, depending on the context. As the documentation says:
Most modules have the name
__builtins__(note the ‘s’) made available as part of their globals. The value of__builtins__is normally either this module or the value of this modules’s__dict__attribute. Since this is an implementation detail, it may not be used by alternate implementations of Python.
In Python 3, __builtin__ has been renamed to builtins, and __builtins__ remains the same (so you should only use builtins in Python 3).
Guido wanted to unite __builtin__ and __builtins__, as you can see here (“Having __builtins__ and __builtin__ both is clearly a bad idea.”) , but apparently nothing came of it.
Apparently the use of __builtins__ is for performance – it gives direct access to __builtin__.__dict__ when used in a non-main module, and therefore removes one level of indirection.
You can understand these like following code.
when cpython is started, cpython load __builtin__ modules into global namespace
import __builtin__as __builtins__
The __builtins__ module should not be confused with the __builtin__ module. The
names, of course, are so similar that it tends to lead to some confusion among new Python
programmers who have gotten this far.
The __builtins__ module consists of a set of builtin names for the built-ins namespace. Most, if not all, of these names come from the
__builtin__ module, which is a module of the built-in functions, exceptions, and other
attributes.
In standard Python execution, __builtins__ contains all the names from
__builtin__. Python used to have a restricted execution model that allowed modification of __builtins__ where key pieces from __builtin__ were left out to create a sandbox environment.
However, due its security flaws and the difficulty involved with repairing it,
restricted execution is no longer supported in Python (as of 2.3).