# Dive Into Python

Python for experienced programmers

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## 1.11. Assigning multiple values at once

One of the cooler programming shortcuts in Python is using sequences to assign multiple values at once.

### Example 1.27. Assigning multiple values at once

    >>> v = ('a', 'b', 'e')
    >>> (x, y, z) = v
    >>> x
    'a'
    >>> y
    'b'
    >>> z
    'e'

| `v` is a tuple of three elements, and `(x, y, z)` is a tuple of three variables. Assigning one to the other assigns each of the values of `v` to each of the variables, in order.

This has all sorts of uses. I often want to assign names to a range of values. In C, you would use `enum` and manually list each constant and its associated value, which seems especially tedious when the values are consecutive. In Python, you can use the built-in `range` function with multi-variable assignment to quickly assign consecutive values.

### Example 1.28. Assigning consecutive values

    >>> range(7)
    [0, 1, 2, 3, 4, 5, 6]
    >>> (MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY) = range(7)
    >>> MONDAY
    0
    >>> TUESDAY
    1
    >>> SUNDAY
    6

| The built-in `range` function returns a list of integers. In its simplest form, it takes an upper limit and returns a `0`-based list counting up to but not including the upper limit. (If you like, you can pass other parameters to specify a base other than `0` and a step other than `1`. You can `print range.__doc__` for details.)
| `MONDAY`, `TUESDAY`, `WEDNESDAY`, `THURSDAY`, `FRIDAY`, `SATURDAY`, and `SUNDAY` are the variables we’re defining. (This example came from the `calendar` module, a fun little module which prints calendars, like the UNIX program `cal`. The `calendar` module defines integer constants for days of the week.)
| Now each variable has its value: `MONDAY` is `0`, `TUESDAY` is `1`, and so forth.

You can also use multi-variable assignment to build functions that return multiple values, simply by returning a tuple of all the values. The caller can treat it as a tuple, or assign the values to individual variables. Many standard Python libraries do this, including the `os` module, which we’ll discuss in chapter 3.

### Further reading

- How to Think Like a Computer Scientist shows how to use multi-variable assignment to swap the values of two variables.