Function templates in python

Question

I would like to know how would I use similar code to template < typename T> in python, as it is used in the C++ code example:

template <typename T>
unsigned int counting_bit(unsigned int v){
   v = v - ((v >> 1) & (T)~(T)0/3);                           // temp
   v = (v & (T)~(T)0/15*3) + ((v >> 2) & (T)~(T)0/15*3);      // temp
   v = (v + (v >> 4)) & (T)~(T)0/255*15;                      // temp
   return v;
}

How would I typecast objects with variable typename in python the same way as it is mentioned in C++?

Even with C++, is `template` required for counting number of bits? There is a `n & (n - 1)` trick for counting bits using loop. — iammilind, Aug 09 '16 at 06:33
@VaibhavBajaj I have not written the python code yet as i am still trying to figure out how to typecast the objects. — Muhammad Ali Qadri, Aug 09 '16 at 06:35
What are you gonna pass as `T` in python? There is only one integer type in python by default, are you going to use `ctypes`? — Holt, Aug 09 '16 at 06:38
@Holt i will pass ctypes, also i find the answer by DeepSpace quite helpful. — Muhammad Ali Qadri, Aug 09 '16 at 06:44

martineau · Answer 1 · 2022-01-04T21:13:45.307

DeepSpace's answer could be embellished to make things more C++-like by using Python's closures to do something like the following — sometimes called a factory function or a function factory — to create functions for specific types by applying the template. It also shows how easy it is in Python to obtain and use the type of another variable.

def converter_template(typename):
    def converter(v):
        t = typename(v)  # convert to numeric for multiply
        return type(v)(t * 2)  # value returned converted back to original type

    return converter

int_converter = converter_template(int)
float_converter = converter_template(float)

print('{!r}'.format(int_converter('21')))    # '42'
print('{!r}'.format(float_converter('21')))  # '42.0'

score 6 · Accepted Answer · answered Aug 09 '16 at 06:32

6

Just pass the type to the function.

For example, see this (useless) function:

def converter(x, required_type):
    return required_type(x)

converter('1', int)
converter('1', float)

answered Aug 09 '16 at 06:32

DeepSpace

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this a good solution and has helped me easily. I wanted to know weather if i could pass ctypes datatypes and return like for example **c_int().value**? – Muhammad Ali Qadri Aug 09 '16 at 06:48
You can pass and return any python object. – cdarke Aug 09 '16 at 06:53

Function templates in python

2 Answers2