¿Hay una forma pitónica de saber cuándo se pasa el primer y último circuito en un
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28-10-2019 - |
Pregunta
Tengo una plantilla en la que coloqué, digamos 5 formularios, pero todos deshabilitados para ser publicados, excepto el primero. El siguiente formulario solo se puede llenar si hago clic en un botón que lo habilite primero.
Estoy buscando una manera de implementar una variable de Templatetag tipo Django.
Básicamente, lo que necesito hacer es algo así:
for form_data in step.hashes:
# get and fill the current form with data in form_data
if not forloop.last:
# click the button that enables the next form
# submit all filled forms
Solución
Si entiendo su pregunta correctamente, ¿desea una prueba simple para si está al principio o al final de la lista?
Si ese es el caso, esto lo haría:
for item in list:
if item != list[-1]:
#Do stuff
Para el primer elemento de la lista, reemplazaría "-1" con 0.
Otros consejos
No conozco nada incorporado, pero puede escribir fácilmente un generador para brindarle la información requerida:
def firstlast(seq):
seq = iter(seq)
el = prev = next(seq)
is_first = True
for el in seq:
yield prev, is_first, False
is_first = False
prev = el
yield el, is_first, True
>>> list(firstlast(range(4)))
[(0, True, False), (1, False, False), (2, False, False), (3, False, True)]
>>> list(firstlast(range(0)))
[]
>>> list(firstlast(range(1)))
[(0, True, True)]
>>> list(firstlast(range(2)))
[(0, True, False), (1, False, True)]
>>> for count, is_first, is_last in firstlast(range(3)):
print(count, "first!" if is_first else "", "last!" if is_last else "")
0 first!
1
2 last!
Podrías usar enumerate
y compare el contador con la longitud de la lista:
for i, form_data in enumerate(step.hashes):
if i < len(step.hashes):
whatever()
for form_data in step.hashes[:-1]:
# get and fill the current form with data in form_data
for form_data in step.hashes[-1:]:
# get and fill the current form with data in form_data
# click the button that enables the next form
# submit all filled forms
No me gusta la repetición de get and fill the current form with data in form_data
? Definir una función.
Generador con búfer.
def first_last( iterable ):
i= iter(iterable)
f= next(i)
yield f, "first"
n= next(i)
for another in i:
yield n, None
n= another
yield n, "last"
for item, state in first_list( iterable ):
# state is "first", None or "last".
Zapante de dos secuencias
flags = ["first"] + (len(iterable)-2)*[None] + ["last"]
for item, state in zip( iterable, flags ):
# state is "first", None or "last".
Creo que quiere tener un envoltorio alrededor del iterador que proporciona las primeras / últimas consultas, también el parámetro podría ser un iterador, por lo que todo tipo de len () fallaría
Aquí es lo que surgí hasta ahora, el truco es usar un doble iterador, uno que mira hacia adelante un paso del primero:
class FirstLastIter(object):
def __init__(self, seq):
self._seq_iter = iter(seq)
self._seq_iter_next = iter(seq)
self._idx = -1
self._last = None
self.next_next()
@property
def first(self):
return self._idx == 0
@property
def last(self):
return self._last == True
def __iter__(self):
return self
def next_next(self):
try:
self._seq_iter_next.next()
except StopIteration:
self._last = True
def next(self):
val = self._seq_iter.next()
self._idx += 1
self.next_next()
return val
for x in FirstLastIter([]):
print x
iterator = FirstLastIter([1])
for x in iterator:
print x,iterator.first,iterator.last
iterator = FirstLastIter([1,2,3])
for x in iterator:
print x,iterator.first,iterator.last
devoluciones:
1 True True
1 True False
2 False False
3 False True
Antes de que alguien aguante sus antorchas o encienda las camtadas, no soy un experto en lo que es Pitónico, que dijo, me parece que si first
y/o last
es buscado de una lista, en el desde entonces if first
o if last
Dentro de un bucle, parece esperado super
la clase y el complemento de la funcionalidad que se desea ... tal vez, entonces lo que sigue es la versión totalmente prealpha E-1^11% de código que puede causar estragos si se mira el martes de la manera correcta. .
import sys
## Prevent `.pyc` (Python byte code) files from being generated
sys.dont_write_bytecode = True
from collections import OrderedDict
class MetaList(list):
"""
Generates list of metadata dictionaries for list types
## Useful resources
- [C Source for list](https://github.com/python/cpython/blob/master/Objects/listobject.c)
- [Supering `list` and `collections.MutableSequence`](https://stackoverflow.com/a/38446773/2632107)
"""
# List supering methods; maybe buggy but seem to work so far...
def __init__(self, iterable = [], **kwargs):
"""
> Could not find what built in `list()` calls the initialized lists during init... might just be `self`...
> If feeling cleverer check the C source. For now this class will keep a copy
## License [GNU_GPL-2](https://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html)
Generates list of metadata dictionaries for lists types
Copyright (C) 2019 S0AndS0
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; version 2
of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
"""
self.metadata = []
for index, value in enumerate(iterable):
if isinstance(value, list):
sub_kwargs = {}
sub_kwargs.update(kwargs)
sub_kwargs['address'] = kwargs.get('address', [index])
sub_list = MetaList(iterable = value, **sub_kwargs)
self.append(sub_list, **kwargs)
else:
self.append(value, **kwargs)
# Note; supering order matters when using built in methods during init
super(MetaList, self).__init__(iterable)
def __add__(self, other):
"""
Called when adding one list to another, eg `MetaList([1,2,3]) + [9,8,7]`
- Returns copy of list plus `other`, sorta like `self.extend` but without mutation
## Example input
test_list = MetaList([1 ,2, 3])
longer_list = test_list + [4, 5, 6]
## Example output
print("#\ttest_list -> {0}".format(test_list))
# test_list -> [1, 2, 3]
print("#\tlonger_list -> {0}".format(longer_list))
# longer_list -> [1, 2, 3, 4, 5, 6]
"""
super(MetaList, self).__add__(other)
output = MetaList(self)
output.extend(other)
return output
def __setitem__(self, index, item, **kwargs):
"""
Called when setting values by index, eg `listing[0] = 'value'`, this updates `self` and `self.metadata`
"""
super(MetaList, self).__setitem__(index, item)
address = kwargs.get('address', []) + [index]
value = item
dictionary = self.__return_dictionary(
address = address,
index = index,
value = value)
self.metadata[index] = dictionary
self.__refresh_first()
self.__refresh_last()
self.__refresh_indexes(start = index)
def append(self, item, **kwargs):
"""
Appends to `self.metadata` an `OrderedDict` with the following keys
- `address`: `[0]` or `[0, 1, 5]` list of indexes mapping to `value`
- `index`: `0` or `42` integer of index within current listing
- `value`: `string`, `['list']`, `{'dict': 'val'}`, etc; not enabled by default
- `first`: `True`/`False` boolean; item is first in current listing
- `last`: `True`/`False` boolean; item is last in current listing
"""
super(MetaList, self).append(item)
# Update last status of previously last item within `self.metadata`
if self.metadata:
self.metadata[-1]['last'] = False
index = len(self.metadata)
address = kwargs.get('address', []) + [index]
value = item
dictionary = self.__return_dictionary(
address = address,
index = index,
value = value)
dictionary['first'] = False
dictionary['last'] = True
if len(self.metadata) == 0:
dictionary['first'] = True
self.metadata += [dictionary]
def extend(self, listing, **kwargs):
"""
Extends `self.metadata` with data built from passed `listing`
- Returns: `None`
> `kwargs` is passed to `MetaList` when transmuting list types
"""
super(MetaList, self).extend(listing)
for index, value in enumerate(listing):
if isinstance(value, list):
last_address = []
if self.metadata:
# Grab `address` list minus last item
last_address = self.metadata[-1]['address'][0:-1]
# Add this `index` to `address` list for recursing
sub_list = MetaList(value, address = last_address + [index], **kwargs)
self.append(sub_list, **kwargs)
else:
self.append(value, **kwargs)
def insert(self, index, item, **kwargs):
"""
Inserts `item` at `index` for `self` and dictionary into `self.metadata`
- Returns: `None`
Note: `self.metadata[index + 1]` have the following data mutated
- `data['index']`
- `data['address']`
Additionally: `self.metadata[0]` and `self.metadata[-1]` data mutations will occur
- `data['first']`
- `data['last']`
"""
super(MetaList, self).insert(index, item)
address = kwargs.get('address', []) + [index]
dictionary = self.__return_dictionary(
address = address,
index = index,
value = item,
**kwargs)
self.metadata.insert(index, dictionary)
self.__refresh_first()
self.__refresh_last()
self.__refresh_indexes(start = index)
# Off-set to avoid n +- 1 errors ;-)
self.__refresh_addresses(
start = index + 1,
index = len(address) - 1,
modifier = 1)
def pop(self, index = -1, target = None):
"""
Pop value from `self` and `self.metadata`, at `index`
- Returns: `self.pop(i)` or `self.metadata.pop(i)` depending on `target`
"""
popped_self = super(MetaList, self).pop(index)
popped_meta = self.__pop_metadata(index)
if 'metadata' in target.lower():
return popped_meta
return popped_self
def remove(self, value):
"""
Removes `value` from `self` and `self.metadata` lists
- Returns: `None`
- Raises: `ValueError` if value does not exsist within `self` or `self.metadata` lists
"""
super(MetaList, self).remove(value)
productive = False
for data in self.metadata:
if data['value'] == value:
productive = True
self.__pop_metadata(data['index'])
break
if not productive:
raise ValueError("value not found in MetaList.metadata values")
# Special herbs and spices for keeping the metadata fresh
def __pop_metadata(self, index = -1):
"""
Pops `index` from `self.metadata` listing, last item if no `index` was passed
- Returns: `<dictionary>`
- Raises: `IndexError` if `index` is outside of listed range
"""
popped_metadata = self.metadata.pop(index)
addr_index = len(popped_metadata['address']) - 1
## Update values within `self.metadata` dictionaries
self.__refresh_first()
self.__refresh_last()
self.__refresh_indexes(start = index)
self.__refresh_addresses(start = index, index = addr_index, modifier = -1)
return popped_metadata
def __return_dictionary(self, address, index, value, **kwargs):
"""
Returns dictionaries for use in `self.metadata` that contains;
- `address`: list of indexes leading to nested value, eg `[0, 4, 2]`
- `index`: integer of where value is stored in current listing
- `value`: Duck!... Note list types will be converted to `MetaList`
- `first`: boolean `False` by default
- `last`: boolean `False` by default
> `kwargs`: passes through to `MetaList` if transmuting a list `value`
"""
if isinstance(value, list):
kwargs['address'] = address
value = MetaList(value, **kwargs)
dictionary = OrderedDict()
dictionary['address'] = address
dictionary['index'] = index
dictionary['value'] = value
dictionary['first'] = False
dictionary['last'] = False
return dictionary
def __refresh_indexes(self, start = 0):
"""
Update indexes from `start` till the last
- Returns: `None`
"""
for i in range(start, len(self.metadata)):
self.metadata[i]['index'] = i
def __refresh_addresses(self, start = 0, end = None, index = 0, modifier = -1):
"""
Updates `address`es within `self.metadata` recursively
- Returns: `None`
- Raises: `TODO`
> `index` is the *depth* within `address` that `modifier` will be applied to
"""
if not start or start < 0:
start = 0
if not end or end > len(self.metadata):
end = len(self.metadata)
for i in range(start, end):
metadata = self.metadata[i]
if isinstance(metadata['value'], list):
metadata['value'].__refresh_addresses(index = index, modifier = modifier)
else:
if len(metadata['address']) - 1 >= index:
metadata['address'][index] += modifier
else:
raise Exception("# TODO: __refresh_addresses append or extend address list")
def __refresh_last(self, quick = True):
"""
Sets/re-sets `self.metadata` `last` value
- Returns `True`/`False` based on if `self.metadata` was touched
If `quick` is `False` all items in current listing will be touched
If `quick` is `True` only the last item and second to last items are touched
"""
if not self.metadata:
return False
if len(self.metadata) > 1:
self.metadata[-2]['last'] = False
if not quick and len(self.metadata) > 1:
for i in range(0, len(self.metadata) - 1):
self.metadata[i]['last'] = False
self.metadata[-1]['last'] = True
return True
def __refresh_first(self, quick = True):
"""
Sets first dictionary within `self.metadata` `first` key to `True`
- Returns `True`/`False` based on if `self.metadata` was touched
If `quick` is `False` all items will be touched in current listing
If `quick` is `True` the first and second items are updated
"""
if not self.metadata:
return False
if len(self.metadata) > 1:
self.metadata[1]['first'] = False
if not quick and len(self.metadata) > 1:
for i in range(1, len(self.metadata)):
self.metadata[i]['first'] = False
self.metadata[0]['first'] = True
return True
# Stuff to play with
def deep_get(self, indexes, iterable = None):
"""
Loops over `indexes` returning inner list or value from `self.metadata`
- `indexes` list of indexes, eg `[1, 3, 2]`
- `iterable` maybe list, if not provided `self.metadata` is searched
"""
referance = self.metadata
if iterable:
reference = iterable
for index in indexes:
reference = reference[index]
return reference
def copy_metadata(self):
"""
Returns copy of `self.metadata`
"""
return list(self.metadata)
def yield_metadata(self, iterable = None, skip = {'first': False, 'last': False, 'between': False}, **kwargs):
"""
Yields a *flat* representation of `self.metadata`,
Prefilter via `skip = {}` dictionary with the following data
- `first`: boolean, if `True` skips items that are first
- `last`: boolean, if `True` skips items that are last
- `between`: boolean, if `True` skips items that are not last or first
"""
metadata = self.metadata
if iterable:
metadata = MetaList(iterable).metadata
for item in metadata:
if isinstance(item.get('value'), list):
# Recurse thy self
for data in item['value'].yield_metadata(skip = skip, **kwargs):
yield data
else:
if skip:
if skip.get('first', False) and item['first']:
continue
if skip.get('last', False) and item['last']:
continue
if skip.get('between', False) and not item['first'] and not item['last']:
continue
# If not skipped get to yielding
yield item
... y tal vez es más buggug que las lámparas de ese amigo que habló públicamente de encuentros cercanos, saben quiénes son ... pero esto hace algunos trucos ingeniosos
Ejemplo de entrada uno
meta_list = MetaList([1, 2, 3, 4, 5])
for data in meta_list.metadata:
if data['first']:
continue
if data['last']:
continue
print("self[{0}] -> {1}".format(data['index'], data['value']))
Ejemplo de salida uno
self[1] -> 2
self[2] -> 3
self[3] -> 4
Ejemplo de entrada dos
meta_list = MetaList(['item one', ['sub item one', ('sub', 'tuple'), [1, 2, 3], {'key': 'val'}], 'item two'])
for data in meta_list.yield_metadata():
address = "".join(["[{0}]".format(x) for x in data.get('address')])
value = data.get('value')
print("meta_list{0} -> {1} <- first: {2} | last: {3}".format(address, value, data['first'], data['last']))
Ejemplo de salida dos
meta_list[0] -> item one <- first: True | last: False
meta_list[1][0] -> sub item one <- first: True | last: False
meta_list[1][1] -> ('sub', 'tuple') <- first: False | last: False
meta_list[1][2][0] -> 1 <- first: True | last: False
meta_list[1][2][1] -> 2 <- first: False | last: False
meta_list[1][2][2] -> 3 <- first: False | last: True
meta_list[1][3] -> {'key': 'val'} <- first: False | last: True
meta_list[2] -> item two <- first: False | last: True
Si sientes que tus cerebros se vuelven frescos, pero no está totalmente bien y eso está a su manera mejor ... para mí, ese es el más Pitónico
Disfruta, y tal vez si hay interés, empujaré esto a Github para que todos tiren y tengan un bifurcado.
Nota al margen @fabriziom +1 para un uso excelente de
@property
mágica