Hat Python eine unveränderliche Liste?

Hat python unveränderliche Listen?

Angenommen, ich möchte die Funktionalität einer geordneten Sammlung von Elementen haben, aber die ich garantieren möchte, wird sich nicht ändern, wie kann das umgesetzt werden? Listen sind bestellt, aber sie können mutiert werden.

4 Solutions collect form web for “Hat Python eine unveränderliche Liste?”

Ja. Es heißt ein tuple .

Also, anstatt [1,2] was eine list und die mutiert sein kann, ist (1,2) ein tuple und kann nicht.


Weitere Informationen:

Ein Ein-Element- tuple kann nicht durch Schreiben (1) instanziiert werden, stattdessen müssen Sie schreiben (1,) . Dies liegt daran, dass der Dolmetscher verschiedene andere Verwendungen für Klammern hat.

Sie können auch Klammern ganz ausschließen: 1,2 ist das gleiche wie (1,2)

Beachten Sie, dass ein Tupel nicht genau eine unveränderliche Liste ist. Klicken Sie hier, um mehr über die Unterschiede zwischen Listen und Tupeln zu erfahren

Aber wenn es ein Tupel von Arrays und Tupel gibt, dann kann das Array innerhalb eines Tupels geändert werden.

 >>> a ([1, 2, 3], (4, 5, 6)) >>> a[0][0] = 'one' >>> a (['one', 2, 3], (4, 5, 6)) 

Hier ist eine unveränderliche Umsetzung. Die zugrunde liegende Liste ist in keinem direkten Datenelement ausgesetzt. Dennoch kann man mit der Verschlusseigenschaft der Memberfunktion aufrufen. Wenn wir dem Konvent folgen, dass wir den Inhalt der Schließung nicht mit der obigen Eigenschaft ändern, wird diese Implementierung dem Zweck dienen. Instanz dieser ImmutableList-Klasse kann überall verwendet werden, wo eine normale Python-Liste erwartet wird.

 from functools import reduce __author__ = 'hareesh' class ImmutableList: """ An unmodifiable List class which uses a closure to wrap the original list. Since nothing is truly private in python, even closures can be accessed and modified using the __closure__ member of a function. As, long as this is not done by the client, this can be considered as an unmodifiable list. This is a wrapper around the python list class which is passed in the constructor while creating an instance of this class. The second optional argument to the constructor 'copy_input_list' specifies whether to make a copy of the input list and use it to create the immutable list. To make the list truly immutable, this has to be set to True. The default value is False, which makes this a mere wrapper around the input list. In scenarios where the input list handle is not available to other pieces of code, for modification, this approach is fine. (Eg, scenarios where the input list is created as a local variable within a function OR it is a part of a library for which there is no public API to get a handle to the list). The instance of this class can be used in almost all scenarios where a normal python list can be used. For eg: 01. It can be used in a for loop 02. It can be used to access elements by index ie immList[i] 03. It can be clubbed with other python lists and immutable lists. If lst is a python list and imm is an immutable list, the following can be performed to get a clubbed list: ret_list = lst + imm ret_list = imm + lst ret_list = imm + imm 04. It can be multiplied by an integer to increase the size (imm * 4 or 4 * imm) 05. It can be used in the slicing operator to extract sub lists (imm[3:4] or imm[:3] or imm[4:]) 06. The len method can be used to get the length of the immutable list. 07. It can be compared with other immutable and python lists using the >, <, ==, <=, >= and != operators. 08. Existence of an element can be checked with 'in' clause as in the case of normal python lists. (eg '2' in imm) 09. The copy, count and index methods behave in the same manner as python lists. 10. The str() method can be used to print a string representation of the list similar to the python list. """ @staticmethod def _list_append(lst, val): """ Private utility method used to append a value to an existing list and return the list itself (so that it can be used in funcutils.reduce method for chained invocations. @param lst: List to which value is to be appended @param val: The value to append to the list @return: The input list with an extra element added at the end. """ lst.append(val) return lst @staticmethod def _methods_impl(lst, func_id, *args): """ This static private method is where all the delegate methods are implemented. This function should be invoked with reference to the input list, the function id and other arguments required to invoke the function @param list: The list that the Immutable list wraps. @param func_id: should be the key of one of the functions listed in the 'functions' dictionary, within the method. @param args: Arguments required to execute the function. Can be empty @return: The execution result of the function specified by the func_id """ # returns iterator of the wrapped list, so that for loop and other # functions relying on the iterable interface can work. _il_iter = lambda: lst.__iter__() _il_get_item = lambda: lst[args[0]] # index access method. _il_len = lambda: len(lst) # length of the list _il_str = lambda: lst.__str__() # string function # Following represent the >, < , >=, <=, ==, != operators. _il_gt = lambda: lst.__gt__(args[0]) _il_lt = lambda: lst.__lt__(args[0]) _il_ge = lambda: lst.__ge__(args[0]) _il_le = lambda: lst.__le__(args[0]) _il_eq = lambda: lst.__eq__(args[0]) _il_ne = lambda: lst.__ne__(args[0]) # The following is to check for existence of an element with the # in clause. _il_contains = lambda: lst.__contains__(args[0]) # * operator with an integer to multiply the list size. _il_mul = lambda: lst.__mul__(args[0]) # + operator to merge with another list and return a new merged # python list. _il_add = lambda: reduce( lambda x, y: ImmutableList._list_append(x, y), args[0], list(lst)) # Reverse + operator, to have python list as the first operand of the # + operator. _il_radd = lambda: reduce( lambda x, y: ImmutableList._list_append(x, y), lst, list(args[0])) # Reverse * operator. (same as the * operator) _il_rmul = lambda: lst.__mul__(args[0]) # Copy, count and index methods. _il_copy = lambda: lst.copy() _il_count = lambda: lst.count(args[0]) _il_index = lambda: lst.index( args[0], args[1], args[2] if args[2] else len(lst)) functions = {0: _il_iter, 1: _il_get_item, 2: _il_len, 3: _il_str, 4: _il_gt, 5: _il_lt, 6: _il_ge, 7: _il_le, 8: _il_eq, 9: _il_ne, 10: _il_contains, 11: _il_add, 12: _il_mul, 13: _il_radd, 14: _il_rmul, 15: _il_copy, 16: _il_count, 17: _il_index} return functions[func_id]() def __init__(self, input_lst, copy_input_list=False): """ Constructor of the Immutable list. Creates a dynamic function/closure that wraps the input list, which can be later passed to the _methods_impl static method defined above. This is required to avoid maintaining the input list as a data member, to prevent the caller from accessing and modifying it. @param input_lst: The input list to be wrapped by the Immutable list. @param copy_input_list: specifies whether to clone the input list and use the clone in the instance. See class documentation for more details. @return: """ assert(isinstance(input_lst, list)) lst = list(input_lst) if copy_input_list else input_lst self._delegate_fn = lambda func_id, *args: \ ImmutableList._methods_impl(lst, func_id, *args) # All overridden methods. def __iter__(self): return self._delegate_fn(0) def __getitem__(self, index): return self._delegate_fn(1, index) def __len__(self): return self._delegate_fn(2) def __str__(self): return self._delegate_fn(3) def __gt__(self, other): return self._delegate_fn(4, other) def __lt__(self, other): return self._delegate_fn(5, other) def __ge__(self, other): return self._delegate_fn(6, other) def __le__(self, other): return self._delegate_fn(7, other) def __eq__(self, other): return self._delegate_fn(8, other) def __ne__(self, other): return self._delegate_fn(9, other) def __contains__(self, item): return self._delegate_fn(10, item) def __add__(self, other): return self._delegate_fn(11, other) def __mul__(self, other): return self._delegate_fn(12, other) def __radd__(self, other): return self._delegate_fn(13, other) def __rmul__(self, other): return self._delegate_fn(14, other) def copy(self): return self._delegate_fn(15) def count(self, value): return self._delegate_fn(16, value) def index(self, value, start=0, stop=0): return self._delegate_fn(17, value, start, stop) def main(): lst1 = ['a', 'b', 'c'] lst2 = ['p', 'q', 'r', 's'] imm1 = ImmutableList(lst1) imm2 = ImmutableList(lst2) print('Imm1 = ' + str(imm1)) print('Imm2 = ' + str(imm2)) add_lst1 = lst1 + imm1 print('Liist + Immutable List: ' + str(add_lst1)) add_lst2 = imm1 + lst2 print('Immutable List + List: ' + str(add_lst2)) add_lst3 = imm1 + imm2 print('Immutable Liist + Immutable List: ' + str(add_lst3)) is_in_list = 'a' in lst1 print("Is 'a' in lst1 ? " + str(is_in_list)) slice1 = imm1[2:] slice2 = imm2[2:4] slice3 = imm2[:3] print('Slice 1: ' + str(slice1)) print('Slice 2: ' + str(slice2)) print('Slice 3: ' + str(slice3)) imm1_times_3 = imm1 * 3 print('Imm1 Times 3 = ' + str(imm1_times_3)) three_times_imm2 = 3 * imm2 print('3 Times Imm2 = ' + str(three_times_imm2)) # For loop print('Imm1 in For Loop: ', end=' ') for x in imm1: print(x, end=' ') print() print("3rd Element in Imm1: '" + imm1[2] + "'") # Compare lst1 and imm1 lst1_eq_imm1 = lst1 == imm1 print("Are lst1 and imm1 equal? " + str(lst1_eq_imm1)) imm2_eq_lst1 = imm2 == lst1 print("Are imm2 and lst1 equal? " + str(imm2_eq_lst1)) imm2_not_eq_lst1 = imm2 != lst1 print("Are imm2 and lst1 different? " + str(imm2_not_eq_lst1)) # Finally print the immutable lists again. print("Imm1 = " + str(imm1)) print("Imm2 = " + str(imm2)) # The following statemetns will give errors. # imm1[3] = 'h' # print(imm1) # imm1.append('d') # print(imm1) if __name__ == '__main__': main() 

Anstelle von Tupel können Sie Frozenset verwenden. Frozenset schafft ein unveränderliches Set. Sie können die Liste als Mitglied der Frozenset und Zugriff auf jedes Element der Liste in frozenset mit Single für Loop.

Python ist die beste Programmiersprache der Welt.