# Summing Numeric Values and Concatenating Sequences

**00:00**
Summing Numeric Values and Concatenation. The primary purpose of `sum()`

is to provide a Pythonic way to add numeric values together. Up to this point, you’ve seen how to use the function to sum integer numbers. Additionally, you can use `sum()`

with any other numeric Python types, such as `float`

, `complex`

, `decimal.Decimal`

, and `fractions.Fraction`

.

**00:28**
On-screen are a few examples of using `sum()`

with values of different numeric types.

**00:40**
First, `sum()`

is used with floating-point numbers. It’s worth noting the function’s behavior when you use the special symbols `inf`

and `nan`

.

**00:50**
The first symbol represents an infinite value, so `sum()`

returns `inf`

. The second symbol, `NaN`

, represents Not a Number values.

**00:59**
Since you can’t add numbers with non-numbers, you get `nan`

as a result. You can also use `sum()`

with complex numbers, decimals,

**01:25**
In all cases, `sum()`

returns the resulting cumulative sum using the appropriate numeric type. Even though `sum()`

is mostly intended to operate on numeric values, you can also use the function to concatenate sequences such as lists and tuples.

**01:44**
To do that, you need to provide an appropriate value to `start`

.

**01:52**
If you supply an inappropriate value, you’ll get a `TypeError`

. You can perform the equivalent concatenation manually. Concatenating lists and tuples is an interesting feature that you can use to flatten a list of lists or a tuple of tuples. As you’ve already seen, the key requirement for these examples to work is to select an appropriate value for `start`

. To concatenate lists then, `start`

needs to hold a list.

**02:25**
`sum()`

is internally performing a concatenation operation, so it works with only those sequence types that support concatenation, with the exception of strings.

**02:37**
When you try to use `sum()`

to concatenate strings, you get a `TypeError`

. As the exception message suggests, you should use the `str.join()`

method to concatenate strings in Python.

**02:50**
You’ll see examples of using this method later on in the course when you’ll see some alternatives to using `sum()`

. But before that, in the next section, you’ll get more practice of using `sum()`

.

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