functional programming – Python equivalents to LINQ

functional programming – Python equivalents to LINQ

The following Python lines should be equivalent to what you have (assuming func, or lambda in your code, returns a Boolean):

# Any
contains = any(func(x) for x in enumerable)

# Count
count = sum(func(x) for x in enumerable)

# Distinct: since we are using a custom comparer here, we need a loop to keep 
# track of what has been seen already
distinct = []
seen = set()
for x in enumerable:
    comp = comparer(x)
    if not comp in seen:
        seen.add(comp)
        distinct.append(x)

# First
element = next(iter(enumerable))

# Except
except_ = [x for x in enumerable if not comparer(x) in other]

References:

• List comprehensions
• Generator expressions
• any() built-in function
• sum() built-in function
• set type

Note that I renamed lambda to func since lambda is a keyword in Python, and I renamed except to except_ for the same reason.

Note that you could also use map() instead of the comprehensions/generators, but it is generally considered less readable.

The original question was how to achieve the same functionality with iterables in Python. As much as I enjoy list comprehensions, I still find LINQ more readable, intuitive and concise in many situations. The following libraries wrap Python iterables to achieve the same functionality in Python with the same LINQ semantics:

• py_linq
• Linq

If you want to stick with built in Python functionality, this blog post provides a fairly thorough mapping of C# LINQ functionality to built-in Python commands.

functional programming – Python equivalents to LINQ

We have generator expressions and various functions for expressing arbitrary conditions over iterables.

any(some_function(e) for e in iterable)
sum(1 for e in iterable if some_function(e))
set(iterable)
next(iterable)
(e for e in iterable if not comparer(e) in other)

would roughly correspond to how you write your examples in idiomatic Python.