pass function as parameter in python

Salvador Dali:

Suppose I want to calculate the following f(f(...f(x)..).
Basically, many functions themselves.
Currently, I am doing the following to achieve this result (and return all intermediate steps):

def iterator(function, x, n=4):
    x = float(x)
    arr = []
    for i in range(n + 1):
        arr.append(x)
        x = function(x)

    return arr

def funcM(x):
    return x / 4 + 12

Then pass the function as funcMa parameter :
print iterator(funcM, 100, 5).

There is nothing wrong with this approach, the calculation is correct.

However, is there a way to do it without defining the function funcM?
Possibly passing a lambda function as a parameter to an iterator function (sorry if it doesn't make sense, I don't really know what a lambda function is).

Max Noel:

A lambda function (or more precisely, a lambda expression ) is just a function that you can define on the spot where you need it. E.g,

f = lambda x: x * 2

exactly the same as

def f(x):
    return x * 2

When I say exactly, I mean it - they disassemble to the same bytecode. The only difference between the two is that the names defined in the second example have names.

Lambda expressions become useful because creating a not statement means, as others have already answered, you can do

print iterator(lambda x: x / 4 + 12, 100, 5)

get what you want.

However, the main difference between lambda expressions and regular functions is that lambdas are more restricted. Lambdas can only contain expressions , not statements. An expression is anything you can put on the right side of an =assignment . (If you want more knowledge, Python defines expressions as http://docs.python.org/2/reference/expressions.html )

This means that a lambda expression cannot be assigned to a variable (in fact, it cannot contain local variables at all, except for parameters). It cannot print (unless another function is called to print). It cannot have for loops, while loops, if tests (except for the ternary operator x if cond else y) or try/except blocks.

If you need to do any of these operations, just define a regular function. In fact, anytime you want to use a lambda, think twice. Is the code more readable if using regular functions? Isn't that a lambda expression you want to reuse elsewhere in your code?

In the end, always do what results in the most readable and maintainable code. In terms of performance, there is no difference between a lambda and a regular function.

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Salvador Dali: Suppose I want to calculate the following f(f(...f(x)..). Basically, many functions themselves. Currently, I am doing the following to achieve this result (and return all intermediate steps): def iterator(function, x, n=4): x = float(x)

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Salvador Dali: Suppose I want to calculate the following f(f(...f(x)..). Basically, many functions themselves. Currently, I am doing the following to achieve this result (and return all intermediate steps): def iterator(function, x, n=4): x = float(x)

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