在任何条件下返回true的值？

Question

I have a function that loops through a large dataset. It takes multiple inputs and contains a lot of conditions. For testing, I sometimes like to run the function without certain conditions, but it is a time consuming to uncomment the conditions - which is what I do know.

Is it possible to give the function an input that always makes the condition true - both for strings and numeric values?

A simplified example:

def function(a,b,c....):

    .....

    item = dict(zip(header,row))
    for row in list:
        if item["variable"] == a:
            print row

    ....

    return something

Now I want to print any row.

function(any,b,c...)

I thought about giving it item["variable"] as input, but this does not work.

Answer 1

If you're looking for a function that returns true for any arguments:

def always(*args, **kw):
    return True

If you're looking for an object that always compares == to any object, you can almost do that:

class AlwaysEqual:
    def __eq__(self, other):
        return True

But just almost—if, say, you put this irresistible force of truthiness up against an immovable object of falsity, whoever's on the left will win.

And if you want to overload multiple comparisons in ways that aren't consistent for any plausible value, like making it equal everything and also be less than everything, there's nothing stopping you. (After all, math.nan is not equal to anything, including itself, and that's required by standards written by people who thought it through in great detail, so Python's not going to stop you from doing something similar.)

Answer 2

Split the code into 'debug mode' and 'release mode' and use explicit check in conditions. Stay away from fancy approaches as it will cause more troubles in future.

debug = True


if debug or len(something) > 2:
    # something always on in debug mode
    do_something()

if not debug and len(some_other_thing) > 7:
    # something always off in debug mode
    do_something_else()

Answer 3

Something like this could work.

def function(a,b,c,test=False):

    .....

    item = dict(zip(header,row))
    for row in list:
        if test:
            print row
        else:
            if item["vaariable"] == a:
                print row

    ....

    return something

Answer 4

You could use a function that takes a boolean and returns True if you're running tests, and the boolean's real value otherwise:

def func(x, y, test=False):
    def _bool(b): 
        return True if test else b

    if _bool(foo == x):
        if _bool(bar == y):
            do_something()

Answer 5

I sometimes instrument my programs with a comparable item, turning debug tracing off and on. In your case, imbue each condition with a short-circuiting or on a flag:

all_true = True
# all_true = False
...

    if all_true or item["vaariable"] == a:
...

Do this once; you can now control it by changing the comment mark. Perhaps more useful, you can turn it on and off during the run.

Answer 6

From reading your code I think you need a Python object which when you use == to compare it to any other Python object the result always will be True ;

First you need to define a class the property I mentioned then use one instance of it instead of any to call the function :

class AnyObject(object):
    def __eq__(self, anything):
        return True

1 == AnyObject()
'' == AnyObject()
None == AnyObject()

Your code:

def function(a,b,c....):

    .....

    item = dict(zip(header,row))
    for row in list:
        if item["variable"] == a:
            print row

    ....

    return something

You only need to use an instance of AnyObject class in place of any when you call function :

any = AnyObject()
function(any,b,c...)

Now the condition is true for all the rows!