Error: object of type 'float' has no len

It even has a size in memory, but the len() function is not to parse the size occupied in memory. And neither is the intention, after all his expectation is that he would show the amount of digits that is shown in the number. They are completely different things. The way the data is in memory and how it is shown on the screen - or is stored somewhere for a human to see - is quite different things.

You are seeing a representation of the data in the form of graphic characters that happen to be numeric digits. But the important thing here is that they are characters. What you are seeing is a sequence (string) of characters, that is, you are seeing a string . So to know the size of this string , you have to say you want it. You have to transform the number into type string and then you can use the len() function to know how many characters it has.

The len() function is available for some data types, not for all. The numeric data itself has a size in memory that is an implementation detail. We know it's 4 bytes, but this does not matter most of the time. Len is the contraction of length , that is, length. So it does not provide exactly the size of nothing, but the length. There is a subtle difference there. The length can be obtained in every kind that is a sequence of something. Which is the case of a string .

The simplest way to convert float to string is with the str() :

b = 3.12; len(str(b))

Another way is with repr() :

b = 3.12; len(repr(b))

See running on ideone .

Unlike C, the size of Python objects in memory is abstracted, and at first a Python program does not need to know about it.

Of course it's good to have a notion - and eventually you can optimize something, for example, using namedtuples instead of dictionaries, etc .... The len function is practically a Python operator: it returns the quantity of items in a sequence - and this has nothing to do with the size of the sequence object in memory, nor with the objects within the sequence.

An integer, or float, or other type is not a sequence. A text string is a string, but the value returned by len to it may have no relation to its size in memory: if it is a unicode text object, each character can occupy 4 bytes. If it is a text encoded in utf-8, the characters have variable length in bytes, and so on.

That said, Python has an auxiliary function to tell the size in bytes of an object in memory - in module sys , the function getsizeof .

So you got what you were trying to do:

>>> import sys
>>> b = 3.12
>>> sys.getsizeof(b)
24

And the answer is this: 24 - A Python object of type "float" occupies 24 bytes in memory. The data itself, the number in the specific case of the float in Python is a 64-bit IEEE 754 float - which uses 8 bytes - the other 16 bytes of the float object are metadata used by Python to control the object's life cycle, other things.

As I said before, this information is not very useful. Or your program will have a few floating-point variables - less than 10 or 20, and have some account with them, and in that case that size in bytes on a machine with several hundred megabytes of memory, as is typically machine memory that run Python, is irrelevant, or, if you're working with scientific computing, where the in-memory size of a number can make a difference, you'll be using specialized objects to store their numbers (even though it is essential that mathematical and logical operations over mass data be done in native code). Typically, numpy library arrays are used in code of this type - but you can also use native python stdlib arrays. Either one allows you to specify the exact data type of each element, and then you can choose to use floats of 32 or 64 bits (4 or 8 bytes per number). In the case of numpy there is even support for 128bit floats (16 bytes, but this may be slow, since there is no hardware support in the current CPUs for this type of data).