找到比例为2的组合几何序列号
Find the combination Geometric Sequence number in the ratio of 2
通过给定权限class，有没有更好的方法来附魔我的list_permission方法，我可以找到可用的权限
我尝试过的：
class Permission:
READ = 1
WRITE = 2
EDIT = 4
DELETE = 8
sum = 0
def has_permission(num, perm):
"""
Return boolean for permission checking
>>> has_permission(Permission.Read)
assume sum = 6
False
"""
return num & perm == perm
def add_permission(num, perm):
"""
sum permission number
>>> add_permission(Permission.Read)
sum + 1
"""
return num += perm
def list_permission(num):
pers = (per for per in dir(Permission) if not per.startswith("__"))
lists = []
for value in pers:
if(has_permission(num, getattr(Permission, value))):
lists.append(value)
return lists
> print(list_permission(6))
> # [WRITE, EDIT]
一个小的优化可能是使用 Permission.__dict__ 而不是 dir(Permission)。阅读 this 了解 dir() 和 __dir__ 之间的区别？
def list_permission(num):
lists = []
for key, val in Permission.__dict__.items():
# Changed "__" to "_" in key.startswith.
if not key.startswith("_") and has_permission(num, val):
lists.append(key)
return lists
如果你需要经常访问list_permission并且多用一些内存也无妨，那么做：
def list_permission(num, cache={}):
if num in cache:
return cache[num]
permissions = []
for key, val in Permission.__dict__.items():
# Changed "__" to "_" in key.startswith.
if not key.startswith("_") and has_permission(num, val):
permissions.append(key)
cache[num] = permissions
return permissions
By given permission class, is there any better method to enchant my list_permission method that i can find out available permission
如果可以修改 Permission class，则按照 georg 在 中的建议使用 Enum。
这是 Enum 的一个很好的用例：
from enum import Enum
class Permission(Enum):
READ = 1
WRITE = 2
EDIT = 4
DELETE = 8
然后
def list_permission(num):
return [
p.name
for p in Permission
if has_permission(num, p.value)
]
您要做的是 "interpret" 将一个数值放入其可能的权限集中，并将结果作为此类权限关键字的列表。
解决方案
因为您分配的值 (1, 2, 4, 8) 基本上是 (2**0, 2**1, 2**2, 2**3)，这可以使用 decimal to binary 转换来建模。以下函数 get_permissions(pnum) 将为您提供所需的输出。
get_permissions(pnum = 7, permissions_dict = None)
输出：
['READ', 'WRITE', 'EDIT']
处理边缘案例
当您提供的 pnum 大于最大允许值时，它还会处理边缘情况，在本例中为 15。
get_permissions(pnum = 19, permissions_dict = None)
输出：
WARNING::: MAX allowed value of pnum = 15
['READ', 'WRITE', 'EDIT', 'DELETE']
函数定义：get_permissions()
请注意，如果需要，您可以提供用户指定的 permissions_dict 来扩展此功能的范围。如果提供 permissions_dict，该函数将回退到其中定义的默认值。
permissions_dict = {'READ': 1, 'WRITE': 2, 'EDIT': 4, 'DELETE': 8}
def get_permissions(pnum = 0, permissions_dict = None):
"""
Returns either a None for pnum=0,
Or,
a list of permission KEYWORDS.
pnum = a non-negative integer
permissions_dict: a dictionary specifying the permissions KEYWORDS
>>> If no permissions_dict is specified, it uses
>>> a default permissions dictionary.
"""
if permissions_dict is None:
permissions_dict = {'READ': 1, 'WRITE': 2, 'EDIT': 4, 'DELETE': 8}
# Max allowed value of pnum
pnum_max = np.array(list(permissions_dict.values())).sum()
if pnum==0:
perm = None
else:
if pnum>pnum_max:
print("WARNING::: MAX allowed value of pnum = {}".format(pnum_max))
pnum = pnum_max
permissions = list(permissions_dict.keys())
# Convert Decimal to Binary
# ==> Convert to list of chars
# ==> Keep 4 chars: use str.zfill(4)
# ==> Flip Order
# Logic with Example:
# Dec(7) --> Bin(111)
# ---> `0111`
# ---> ['0','1','1','1']
# ---> ['1','1','1','0']
p = list(str(int(bin(pnum)[2:])).zfill(4))
p.reverse()
# Extract permissions as KEYWORDS
imax = len(permissions)
perm = [permissions[i] for i,x in enumerate(p) if bool(int(x)) and i<imax]
return perm
希望对您有所帮助。
通过给定权限class，有没有更好的方法来附魔我的list_permission方法，我可以找到可用的权限
我尝试过的：
class Permission:
READ = 1
WRITE = 2
EDIT = 4
DELETE = 8
sum = 0
def has_permission(num, perm):
"""
Return boolean for permission checking
>>> has_permission(Permission.Read)
assume sum = 6
False
"""
return num & perm == perm
def add_permission(num, perm):
"""
sum permission number
>>> add_permission(Permission.Read)
sum + 1
"""
return num += perm
def list_permission(num):
pers = (per for per in dir(Permission) if not per.startswith("__"))
lists = []
for value in pers:
if(has_permission(num, getattr(Permission, value))):
lists.append(value)
return lists
> print(list_permission(6))
> # [WRITE, EDIT]
一个小的优化可能是使用 Permission.__dict__ 而不是 dir(Permission)。阅读 this 了解 dir() 和 __dir__ 之间的区别？
def list_permission(num):
lists = []
for key, val in Permission.__dict__.items():
# Changed "__" to "_" in key.startswith.
if not key.startswith("_") and has_permission(num, val):
lists.append(key)
return lists
如果你需要经常访问list_permission并且多用一些内存也无妨，那么做：
def list_permission(num, cache={}):
if num in cache:
return cache[num]
permissions = []
for key, val in Permission.__dict__.items():
# Changed "__" to "_" in key.startswith.
if not key.startswith("_") and has_permission(num, val):
permissions.append(key)
cache[num] = permissions
return permissions
By given permission class, is there any better method to enchant my list_permission method that i can find out available permission
如果可以修改 Permission class，则按照 georg 在 Enum。
这是 Enum 的一个很好的用例：
from enum import Enum
class Permission(Enum):
READ = 1
WRITE = 2
EDIT = 4
DELETE = 8
然后
def list_permission(num):
return [
p.name
for p in Permission
if has_permission(num, p.value)
]
您要做的是 "interpret" 将一个数值放入其可能的权限集中，并将结果作为此类权限关键字的列表。
解决方案
因为您分配的值 (1, 2, 4, 8) 基本上是 (2**0, 2**1, 2**2, 2**3)，这可以使用 decimal to binary 转换来建模。以下函数 get_permissions(pnum) 将为您提供所需的输出。
get_permissions(pnum = 7, permissions_dict = None)
输出：
['READ', 'WRITE', 'EDIT']
处理边缘案例
当您提供的 pnum 大于最大允许值时，它还会处理边缘情况，在本例中为 15。
get_permissions(pnum = 19, permissions_dict = None)
输出：
WARNING::: MAX allowed value of pnum = 15
['READ', 'WRITE', 'EDIT', 'DELETE']
函数定义：get_permissions()
请注意，如果需要，您可以提供用户指定的 permissions_dict 来扩展此功能的范围。如果提供 permissions_dict，该函数将回退到其中定义的默认值。
permissions_dict = {'READ': 1, 'WRITE': 2, 'EDIT': 4, 'DELETE': 8}
def get_permissions(pnum = 0, permissions_dict = None):
"""
Returns either a None for pnum=0,
Or,
a list of permission KEYWORDS.
pnum = a non-negative integer
permissions_dict: a dictionary specifying the permissions KEYWORDS
>>> If no permissions_dict is specified, it uses
>>> a default permissions dictionary.
"""
if permissions_dict is None:
permissions_dict = {'READ': 1, 'WRITE': 2, 'EDIT': 4, 'DELETE': 8}
# Max allowed value of pnum
pnum_max = np.array(list(permissions_dict.values())).sum()
if pnum==0:
perm = None
else:
if pnum>pnum_max:
print("WARNING::: MAX allowed value of pnum = {}".format(pnum_max))
pnum = pnum_max
permissions = list(permissions_dict.keys())
# Convert Decimal to Binary
# ==> Convert to list of chars
# ==> Keep 4 chars: use str.zfill(4)
# ==> Flip Order
# Logic with Example:
# Dec(7) --> Bin(111)
# ---> `0111`
# ---> ['0','1','1','1']
# ---> ['1','1','1','0']
p = list(str(int(bin(pnum)[2:])).zfill(4))
p.reverse()
# Extract permissions as KEYWORDS
imax = len(permissions)
perm = [permissions[i] for i,x in enumerate(p) if bool(int(x)) and i<imax]
return perm
希望对您有所帮助。