如何将元组列表传递给lamda函数

Question

When list of tuples are used in for loop it works perfectly with two separate variables as below

t_dict = {
    "k1": "v1",
    "k2": "v2",
    "k3": "v3",
    "k4": "v4",
    "k5": "v5"
}

for k, v in t_dict.items():
    print "%s=%s" % (k, v)

But when converted into lambda with map function got an error as below

print map(lambda k, v: "%s=%s" % (k, v), t_dict.items())

Traceback (most recent call last):   File "test.py", line 14, in <module>
    print map(lambda k, v: "%s=%s" % (k, v), t_dict.items()) TypeError: <lambda>() takes exactly 2 arguments (1 given)

Is there any other way to call list of tuple in lambda function?

Answer 1

Built-in map supports multiple iterables:

res = map(lambda k, v: "%s=%s" % (k, v), t_dict, t_dict.values())
# ['k1=v1', 'k2=v2', 'k3=v3', 'k4=v4', 'k5=v5']

As described in the docs for map :

If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel.

Answer 2

就您而言，您还可以在%之后使用元组进行格式化，因此：

map(lambda t: "%s=%s" % t, t_dict.items())

Answer 3

As already suggested, you can pass multiple iterables to map , but if you want to pass the items and not keys and values individually, you can use zip(*...) to "transpose" the items to two lists and use * again to pass those as two different arguments to map :

>>> list(map(lambda k, v: "%s=%s" % (k, v), *zip(*t_dict.items())))
['k1=v1', 'k2=v2', 'k3=v3', 'k4=v4', 'k5=v5']

Or use itertools.starmap :

>>> from itertools import starmap
>>> list(starmap(lambda k, v: "%s=%s" % (k, v), t_dict.items()))
['k1=v1', 'k2=v2', 'k3=v3', 'k4=v4', 'k5=v5']

Answer 4

Other option is this way ( str.join(iterable) ) to get the list of strings:

map( lambda t: "=".join(t), t_dict.items() )
#=> ['k3=v3', 'k2=v2', 'k1=v1', 'k5=v5', 'k4=v4']

This version can also print out:

import sys
map( lambda t: sys.stdout.write("=".join(t) + "\n"), t_dict.items() )

# k3=v3
# k2=v2
# k1=v1
# k5=v5
# k4=v4