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...definition above will bind flatten to whatever it was previously bound to. The second will do the same, if it was already bound to the when decorator's first argument. If flatten is unbound or bound to something else, it will be rebound to the function definition as given. The last two definitions above will always bind flatten_basestring to the function definition as given. Using this approach allows you to both give a method a descriptive name (often useful in tracebacks!) and to reuse the ...
...lambda expression directly to an identifier: # Correct: def f(x): return 2*x # Wrong: f = lambda x: 2*x The first form means that the name of the resulting function object is specifically 'f' instead of the generic '<lambda>'. This is more useful for tracebacks and string representations in general. The use of the assignment statement eliminates the sole benefit a lambda expression can offer over an explicit def statement (i.e. that it can be embedded inside a larger expression) Deriv...
...definition in the nearest enclosing function scope will be used. One consequence of this change is that lambda statements could reference variables in the namespaces where the lambda is defined. In some unusual cases, this change will break code. In all previous version of Python, names were resolved in exactly three namespaces -- the local namespace, the global namespace, and the builtin namespace. According to this old definition, if a function A is defined within a function B, the names bo...
...definition and only passes in the __class__ cell when this is found. Thus, calling a global alias of super without arguments will not necessarily work. Closed Issues Determining the class object to use The class object is taken from a cell named __class__. Should super actually become a keyword? No. It is not necessary for super to become a keyword. super used with __call__ attributes It was considered that it might be a problem that instantiating super instances the classic way, because...
...lambda Lambda expression if -- else Conditional expression or Boolean OR and Boolean AND not x Boolean NOT in, not in, is, is not, <, <=, >, >=, !=, == Comparisons, including membership tests and identity tests | Bitwise OR ^ Bitwise XOR & Bitwise AND <<, >> Shifts +, - Addition and subtraction *, @, /, //, % Multiplication, matrix multiplication, division, remainder +x, -x, ~x Positive, negative, bitwise NOT ** Exponentiation await x Await expression x...
...lambda s: zip(*s). That transformation also defines a matrix transpose or an equivalent row/column swap for tables defined as lists of tuples. The latter transformation is commonly used when reading data files with records as rows and fields as columns. For example, the code: date, rain, high, low = zip(*csv.reader(file("weather.csv"))) rearranges columnar data so that each field is collected into individual tuples for straightforward looping and summarization: print "Total rainfall", sum(...
...definition. Parameter.VAR_POSITIONAL - a tuple of positional arguments that aren't bound to any other parameter. This corresponds to a "*args" parameter in a Python function definition. Parameter.VAR_KEYWORD - a dict of keyword arguments that aren't bound to any other parameter. This corresponds to a "**kwargs" parameter in a Python function definition. Always use Parameter.* constants for setting and checking value of the kind attribute. replace(*, name=<optional>, kind=<option...
...definitions cannot be nested. But in Python, though functions are usually defined at the top level, a function definition can be executed anywhere. This gave Python the syntactic appearance of nested scoping without the semantics, and yielded inconsistencies that were surprising to some programmers -- for example, a recursive function that worked at the top level would cease to work when moved inside another function, because the recursive function's own name would no longer be visible in its ...
...definitions. Given a class C in a complicated multiple inheritance hierarchy, it is a non-trivial task to specify the order in which methods are overridden, i.e. to specify the order of the ancestors of C. The list of the ancestors of a class C, including the class itself, ordered from the nearest ancestor to the furthest, is called the class precedence list or the linearization of C. The Method Resolution Order (MRO) is the set of rules that construct the linearization. In the Python literatu...
...definition syntax, you are free to use inheritance, metaclasses, docstrings, user-defined methods, class factories, and other Python class features. A class decorator is provided which inspects a class definition for variables with type annotations as defined in PEP 526, "Syntax for Variable Annotations". In this document, such variables are called fields. Using these fields, the decorator adds generated method definitions to the class to support instance initialization, a repr, comparison met...
...lambdas required in typical callback programming. This convention specifically does not support keyword arguments. Keyword arguments are used to pass optional extra information about the callback. This allows graceful evolution of the API without having to worry about whether a keyword might be significant to a callee somewhere. If you have a callback that must be called with a keyword argument, you can use a lambda. For example: loop.call_soon(lambda: foo('abc', repeat=42)) Coroutines a...
...definitions or iterable unpacking. In all these cases, we find that the syntax for sending and that for receiving 'data' are virtually identical. Assignment targets such as variables, attributes and subscripts: foo.bar[2] = foo.bar[3]; Function definitions: a function defined with def foo(x, y, z=6) is called as, e.g., foo(123, y=45), where the actual arguments provided at the call site are matched against the formal parameters at the definition site; Iterable unpacking: a, b = b, a or [a, b] ...
...definitions of an OO Programming Language? From: Tim Peters <@email.msn.com> Date: Sun, 29 Mar 1998 18:19:54 -0500 [jeff <nospam@myhost.com>] > Is it not true that a programming language must > enforce "data hiding" or encapsulation to be > considered a true Object Oriented programming > language? Absolutely! Guido (van Rossum, Python's creator) probably doesn't even know how to spell those phrases, though. > (It is true incase you thought...
...definition, def "+"(a, b) in place of def __add__(a, b) This appears to require greater syntactical change, and would only be useful when arbitrary additional operators are allowed. Impact on general elementization The distinction between objectwise and elementwise operations are meaningful in other contexts as well, where an object can be conceptually regarded as a collection of elements. It is important that the current proposal does not preclude possible future extensions. O...
...definitions as appropriate. Applications should check for the presence of any variables they require, and have a fallback plan in the event such a variable is absent. Note: missing variables (such as REMOTE_USER when no authentication has occurred) should be left out of the environ dictionary. Also note that CGI-defined variables must be strings, if they are present at all. It is a violation of this specification for a CGI variable's value to be of any type other than str. In addition to the ...
...definitions as appropriate. Applications should check for the presence of any variables they require, and have a fallback plan in the event such a variable is absent. Note: missing variables (such as REMOTE_USER when no authentication has occurred) should be left out of the environ dictionary. Also note that CGI-defined variables must be native strings, if they are present at all. It is a violation of this specification for any CGI variable's value to be of any type other than str. In additio...
...definition to provide additional metadata about each field in the class. This metadata can describe, for example, default values, or indicate whether the field should be included in the synthesized __init__ method. Field descriptors can be omitted in cases where additional metadata is not required: @dataclass class Employee: # Field with no descriptor name: str # Field that uses field descriptor class instance age: Optional[int] = field(default=None, init=False) # Field wi...
...definitions were missing on FreeBSD 5.x unless the __BSD_VISIBLE symbol was defined. configure now defines it as needed. C API Unicode objects now support mbcs as a built-in encoding, so the C API can use it without deferring to the encodings package. Windows The Windows implementation of PyThread_start_new_thread() never checked error returns from Windows functions correctly. As a result, it could claim to start a new thread even when the Microsoft _beginthread() function failed (due ...
...definitions to the CPython C API. Motivation While the precise semantics of the locals() builtin are nominally undefined, in practice, many Python programs depend on it behaving exactly as it behaves in CPython (at least when no tracing functions are installed). Other implementations such as PyPy are currently replicating that behaviour, up to and including replication of local variable mutation bugs that can arise when a trace hook is installed [1]. While this PEP considers CPython's current ...
...definition with a platform- specific spelling in that platform's pyconfig.h. You can also override pyport.h's default Py_IS_INFINITY definition now. C API SF patch 1044089: New function PyEval_ThreadsInitialized() returns non-zero if PyEval_InitThreads() has been called. The undocumented and unused extern int _PyThread_Started was removed. The C API calls PyInterpreterState_New() and PyThreadState_New() are two of the very few advertised as being safe to call without holding the GIL. Howe...