DefaultDict
This is a package for a defaultdict that deep copies its default value.
This can be used to implement a simple counter object, similar to the example code this is based on.
counter = DefaultDict()
for item in ['spam', 'egg', 'spam', 'spam', 'bacon', 'spam']:
counter[item] += 1
print("Menu contents:")
for item in counter:
print(" {}x {}".format(counter[item], item))Output:
Menu contents:
1x bacon
1x egg
4x spam
Unlike collections.defaultdict, the default value is an object - not a factory. This allows for easier creation of nested data structures. For example, the following is valid and encouraged:
# shapes_by_color[color][shape] = count
shapes_by_color = DefaultDict(
default=DefaultDict(
{'total': 0},
default=0
)
)
with open('test/shapes.log', 'r') as fp:
for line in fp:
color, shape = line.split()
shapes_by_color[color][shape] += 1
shapes_by_color[color]['total'] += 1
for color, shapes in shapes_by_color.items():
print("{}:".format(color))
for shape, count in shapes.items():
if shape == 'total':
continue
print(" {}x {}".format(count, shape))
print(" Total: {}".format(count))Output:
green:
2x triangle
1x circle
Total: 3
red:
1x octagon
2x rhombus
Total: 3
blue:
1x triangle
1x square
Total: 2
Note that the default value is a reference, and is affected by external changes. This only affects new uses of the default value, not previous uses.
spam = DefaultDict(default=['Hello'])
print(spam['eggs'])
spam.default.append('world')
print(spam['sausage'])
print(spam)Output:
['Hello']
['Hello', 'world']
DictWithDefault(init={'sausage': ['Hello', 'world'], 'eggs': ['Hello']}, default=['Hello', 'world'])
