In Python, I am trying to sort by date with lambda. I can't understand my error message. The message is:
<lambda>() takes exactly 1 argument (2 given)
The line I have is
a = sorted(a, lambda x: x.modified, reverse=True)
This question is related to
python
sorting
functional-programming
anonymous-function
lst = [('candy','30','100'), ('apple','10','200'), ('baby','20','300')]
lst.sort(key=lambda x:x[1])
print(lst)
It will print as following:
[('apple', '10', '200'), ('baby', '20', '300'), ('candy', '30', '100')]
You're trying to use key functions with lambda functions.
Python and other languages like C# or F# use lambda functions.
Also, when it comes to key functions and according to the documentation
Both list.sort() and sorted() have a key parameter to specify a function to be called on each list element prior to making comparisons.
...
The value of the key parameter should be a function that takes a single argument and returns a key to use for sorting purposes. This technique is fast because the key function is called exactly once for each input record.
So, key functions have a parameter key and it can indeed receive a lambda function.
In Real Python there's a nice example of its usage. Let's say you have the following list
ids = ['id1', 'id100', 'id2', 'id22', 'id3', 'id30']
and want to sort through its "integers". Then, you'd do something like
sorted_ids = sorted(ids, key=lambda x: int(x[2:])) # Integer sort
and printing it would give
['id1', 'id2', 'id3', 'id22', 'id30', 'id100']
In your particular case, you're only missing to write key= before lambda. So, you'd want to use the following
a = sorted(a, key=lambda x: x.modified, reverse=True)
Source: Stackoverflow.com