Optional arguments

Sometimes it is useful to have a single function that can apply to different numbers of arguments.
For example, we might want a function that reads in data from a file that is normally called "data" but could be some other file.
```
>>>read_data()
...
>>>read_data("other_data")
...
```
In Python we indicate optional parameters in the function definition by putting =default_value after the parameter name.
```
def read_data(filename="data"):
...
```
There can be any number of optional parameters, as long as none of them appear before the obligatory parameters in the parameter list.
```
def conjugate(verb, tense="present", person="3", number="singular"):
...
```
When you call a function with optional arguments, you can leave out any or all of the optional arguments. If you refer to the arguments in the same order as in the function definition, you don't need to use the parameter names; otherwise they're required.
```
>>>conjugate('pedir')
>>>conjugate('pedir', 'past')
>>>conjugate('pedir', 'past', '1', 'plural')
>>>conjugate('pedir', person='1')
>>>conjugate('pedir', number='singular', person='1', tense='past')
```

Practice with optional arguments

Here's a dictionary of translations of English adjectives to Spanish adjectives. Notice that the Spanish adjectives have multiple forms corresponding to one English adjective, maximally four (masculine singular and plural, feminine singular and plural).

EN2ES_ADJ = {'happy': {'s': {'m': 'contento', 'f': 'contenta'}, 'p': {'m': 'contentos', 'f': 'contentas'}},
             'sad': {'s': 'triste', 'p': 'tristes'},
             'poor': {'s': 'pobre', 'p': 'pobres'},
             'rich': {'s': {'m': 'rico', 'f': 'rica'}, 'p': {'m': 'ricos', 'f': 'ricas'}}}

Write a function that takes an English adjective and optional number and gender arguments and provides the Spanish translation. With no gender specified, it uses masculine; with no number, it uses plural.
```
>>> en2es_adj('poor')
'pobre'
>>> en2es_adj('rich')
'rico'
>>> en2es_adj('rich', number='p')
'ricos'
>>> en2es_adj('rich', number='p', gender='f')
'ricas'
>>> en2es_adj('good')
There is no entry for good
```

Answer