将可选的文件名和变量传递给Python函数(如果可选kwarg set)

Question

我试图找到一个类似的问题/答案，但努力把任何答案到这个问题，希望有人可以帮助。

我有一个函数，它读取文件名data_dir/filename，从文件中提取data_var，并且还读取**kwargs中的其他参数。必须读入默认的filename和dat_var，函数看起来像

def function(data_dir, filename, data_var, **kwargs):
# some code

然而，我想要添加filename2和data_var2的选项，这也必须伴随着**kwargs来计算额外的数据。

例如，我将定义kwargs = {"lflag" : True}并读入额外的数据，该函数看起来像

def function(data_dir, filename, data_var, filename2, data_var2, **kwargs):

# default flag
opt_dic = {"lflag"  : False}
for key in kwargs:
opt_dic[key] = kwargs[key]
# load in filename and read data_var
ds = Dataset(data_dir + filename)
var = ds.variables[data_var][...]
ds.close()
# load in filename2 and read data_var2
if opt_dic["lflag"]:
ds2 = Dataset(data_dir + filename2)
var2 = ds2.variables[data_var2][...]
ds2.close()
# some more code

但是我如何将filename2和data_var2定义为可选参数，可以在不需要时离开函数?

在默认状态下调用该函数的示例，

kwargs = {}
output = function(data_dir, filename, data_var, **kwargs):

和附加数据

kwargs = {"lflag" : True}
output = function(data_dir, filename, data_var, filename2, data_var2, **kwargs):

Answer 1

考虑在任何情况下只使用一个filename和一个data_var参数。因此，各自的参数可以是字符串或两个字符串的列表。例如，为filename实现这个想法可以这样开始:

def function(data_dir, filename, data_var, **kwargs):

filename2 = None

if type(filename) == list:

if len(filename) != 2:
raise ValueError('filename lists must have exactly two elements.')

filename, filename2 = filename

print(filename, filename2)

# ...

function('/a/', ['f1', 'f2'], 'v1')
>>> f1 f2

Answer 2

*args和* *kwargs

def function(data_dir, filename, data_var, *args, **kwargs)
data_dir = "method argument"
filename = "method argument"
data_var = "method argument"
args     = [] # an iterable
kwargs   = {} # a dictionary key/value pair
print(data_dir, filename, data_var)
print(args)
print(kwargs)

输出示例

>>> function("/tmp", "test.txt", "var-test", "test2.txt", "var2-test", test="arguments-keyvalue") 
/tmp test.txt var-test 
('test2.txt', 'var2-test') 
{'test': 'arguments-keyvalue'}

Real Python explain: here

Answer 3

您不需要kwargs标志;你可以按照

这样做

def function(data_dir, filename, data_var, filename2=None, data_var2=None):
# always perform computations on data_dir and filename
ds = Dataset(data_dir + filename)
var = ds.variables[data_var][...]
ds.close()
# if filename2 was passed, assume data_var2 was passed
if not (filename2 is None):
ds2 = Dateset(data_dir + filename)
var2 = ds2.variables[data_var2][...]

# some more code
...

这里有一个最小的例子来演示

def f(x,y=None)
print(x) # always executed
if not(y is None):
print(y)
f(1) # prints 1
f(1,2) # prints 1 and 2, separated by newlines

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