# Converting Dictionary#

At the moment, the only class contained in this model is a key converting dictionary, which applies some function (e.g. type conversion function) to all arguments used as keys.

AUTHORS:

• Martin von Gagern (2015-01-31): initial version

EXAMPLES:

A `KeyConvertingDict` will apply a conversion function to all method arguments which are keys:

```sage: from sage.misc.converting_dict import KeyConvertingDict
sage: d = KeyConvertingDict(int)
sage: d["3"] = 42
sage: list(d.items())
[(3, 42)]
```

This is used e.g. in the result of a variety, to allow access to the result no matter how a generator is identified:

```sage: K.<x,y> = QQ[]
sage: I = ideal([x^2+2*y-5,x+y+3])
sage: V = sorted(I.variety(AA), key=str)
sage: v = V[0]
sage: v['x'], v['y']
(-2.464101615137755?, -0.535898384862246?)
sage: list(v)[0].parent()
Multivariate Polynomial Ring in x, y over Algebraic Real Field
```
class sage.misc.converting_dict.KeyConvertingDict(key_conversion_function, data=None)#

Bases: `dict`

A dictionary which automatically applies a conversions to its keys.

The most common application is the case where the conversion function is the object representing some category, so that key conversion means a type conversion to adapt keys to that category. This allows different representations for keys which in turn makes accessing the correct element easier.

INPUT:

• `key_conversion_function` – a function which will be applied to all method arguments which represent keys.

• `data` – optional dictionary or sequence of key-value pairs to initialize this mapping.

EXAMPLES:

```sage: from sage.misc.converting_dict import KeyConvertingDict
sage: d = KeyConvertingDict(int)
sage: d["3"] = 42
sage: list(d.items())
[(3, 42)]
sage: d[5.0] = 64
sage: d["05"]
64
```
pop(key, *args)#

Remove and retrieve a given element from the dictionary.

INPUT:

• `key` – A value identifying the element, will be converted.

• `default` – The value to return if the element is not mapped, optional.

EXAMPLES:

```sage: from sage.misc.converting_dict import KeyConvertingDict
sage: d = KeyConvertingDict(int)
sage: d[3] = 42
sage: d.pop("3")
42
sage: d.pop("3", 33)
33
sage: d.pop("3")
Traceback (most recent call last):
...
KeyError: ...
```
setdefault(key, default=None)#

Create a given mapping unless there already exists a mapping for that key.

INPUT:

• `key` – A value identifying the element, will be converted.

• `default` – The value to associate with the key.

EXAMPLES:

```sage: from sage.misc.converting_dict import KeyConvertingDict
sage: d = KeyConvertingDict(int)
sage: d.setdefault("3")
sage: list(d.items())
[(3, None)]
```
update(*args, **kwds)#

Update the dictionary with key-value pairs from another dictionary, sequence of key-value pairs, or keyword arguments.

INPUT:

• `key` – A value identifying the element, will be converted.

• `args` – A single dict or sequence of pairs.

• `kwds` – Named elements require that the conversion function accept strings.

EXAMPLES:

```sage: from sage.misc.converting_dict import KeyConvertingDict
sage: d = KeyConvertingDict(int)
sage: d.update([("3",1),(4,2)])
sage: d[3]
1
sage: d.update({"5": 7, "9": 12})
sage: d[9]
12
sage: d = KeyConvertingDict(QQ['x'])
sage: d.update(x=42)
sage: d
{x: 42}
```