Question: If I have variables `x` and `y`, such that:

* `x` is always a string
* `y` can either be a string or a list of strings

How can I create a list `z == [x, <all elements of y>]`?

For instance:

```
x = 'x'
y = 'y'
# create z
assert z == ['x', 'y']

```

```
x = 'x'
y = ['y', 'y2']
# create z
assert z == ['x', 'y', 'y2']

```

Answer: 
```
z = [x]
if isinstance(y, list):
    z.extend(y)
else:
    z.append(y)

```
```
import itertools
z = itertools.chain(x, y)

```