# Dictionaries
A **dictionary** maps keys to values:
```python
ages = {"Ada": 27, "Linus": 54}
ages["Ada"] # 27
ages["Grace"] = 105 # add a new key
"Linus" in ages # True
```
You can iterate over a dict in three useful ways:
```python
for key in ages: # keys
...
for value in ages.values(): # values
...
for key, value in ages.items(): # both
...
```
## Your task
Write a function `word_counts(words)` that takes a list of strings and
returns a dictionary mapping each word to the number of times it appears
(case-sensitive — `"Hi"` and `"hi"` are different keys).
```python
word_counts(["a", "b", "a", "a", "b", "c"])
# {"a": 3, "b": 2, "c": 1}
word_counts([])
# {}
```