ldict

ldict

A lazy dict.

This project was succeeded by hdict.

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Latest release | Current code | API documentation

See also

• laziness+identity+persistence (idict)

Overview

A ldict is a dict with str keys.

Simple usage example

from ldict import ldict

a = ldict(x=3)
print(a)
"""
{
    "x": 3
}
"""

b = ldict(y=5)
print(b)
"""
{
    "y": 5
}
"""

print(a >> b)
"""
{
    "x": 3,
    "y": 5
}
"""

We consider that every value is generated by a process, starting from an empty ldict. The process is a sequence of transformation steps done through the operator >>, which symbolizes a data flow. There are two types of steps:

• value insertion - represented by dict-like objects
• function application - represented by ordinary python functions

A ldict is completely defined by its key-value pairs so that it can be converted from/to a built-in dict.

Creating a ldict is not different from creating an ordinary dict. Optionally it can be created through the >> operator used after empty:

Function application is done in the same way. The parameter names define the input fields, while the keys in the returned dict define the output fields:

Similarly, for anonymous functions:

Finally, the result is only evaluated at request:

Installation

...as a standalone lib

# Set up a virtualenv. 
python3 -m venv venv
source venv/bin/activate

# Install from PyPI...
pip install --upgrade pip
pip install -U ldict
pip install -U ldict[full]  # use this for extra functionality (recommended)

# ...or, install from updated source code.
pip install git+https://github.com/davips/ldict

...from source

git clone https://github.com/davips/ldict
cd ldict
poetry install

Examples

Merging two ldicts

from ldict import ldict

a = ldict(x=3)
print(a)
"""
{
    "x": 3
}
"""

b = ldict(y=5)
print(b)
"""
{
    "y": 5
}
"""

print(a >> b)
"""
{
    "x": 3,
    "y": 5
}
"""

Lazily applying functions to ldict

from ldict import ldict

a = ldict(x=3)
print(a)
"""
{
    "x": 3
}
"""

a = a >> ldict(y=5) >> {"z": 7} >> (lambda x, y, z: {"r": x ** y // z})
print(a)
"""
{
    "x": 3,
    "y": 5,
    "z": 7,
    "r": "→(x y z)"
}
"""

print(a.r)
"""
34
"""

print(a)
"""
{
    "x": 3,
    "y": 5,
    "z": 7,
    "r": 34
}
"""

Parameterized functions and sampling

from random import Random

from ldict import empty, let


# A function provide input fields and, optionally, parameters.
# For instance:
# 'a' is sampled from an arithmetic progression
# 'b' is sampled from a geometric progression
# Here, the syntax for default parameter values is borrowed with a new meaning.
def fun(x, y, a=[-100, -99, -98, ..., 100], b=[0.0001, 0.001, 0.01, ..., 100000000]):
    return {"z": a * x + b * y}


def simplefun(x, y):
    return {"z": x * y}


# Creating an empty ldict. Alternatively: d = ldict().
d = empty >> {}
print(d)
"""
{}
"""

# Putting some values. Alternatively: d = ldict(x=5, y=7).
d["x"] = 5
d["y"] = 7
print(d)
"""
{
    "x": 5,
    "y": 7
}
"""

# Parameter values are uniformly sampled.
d1 = d >> simplefun
print(d1)
print(d1.z)
"""
{
    "x": 5,
    "y": 7,
    "z": "→(x y)"
}
35
"""

d2 = d >> simplefun
print(d2)
print(d2.z)
"""
{
    "x": 5,
    "y": 7,
    "z": "→(x y)"
}
35
"""

# Parameter values can also be manually set.
e = d >> let(fun, a=5, b=10)
print(e.z)
"""
95
"""

# Not all parameters need to be set.
e = d >> Random() >> let(fun, a=5)
print("e =", e.z)
"""
e = 25.007
"""

# Each run will be a different sample for the missing parameters.
e = e >> Random() >> let(fun, a=5)
print("e =", e.z)
"""
e = 725.0
"""

# We can define the initial state of the random sampler.
# It will be in effect from its location place onwards in the expression.
e = d >> Random(0) >> let(fun, a=5)
print(e.z)
"""
725.0
"""

# All runs will yield the same result,
# if starting from the same random number generator seed.
e = e >> Random(0) >> let(fun, a=[555, 777])
print("Let 'a' be a list:", e.z)
"""
Let 'a' be a list: 700003885.0
"""

# Reproducible different runs are achievable by using a single random number generator.
e = e >> Random(0) >> let(fun, a=[5, 25, 125, ..., 10000])
print("Let 'a' be a geometric progression:", e.z)
"""
Let 'a' be a geometric progression: 700003125.0
"""

rnd = Random(0)
e = d >> rnd >> let(fun, a=5)
print(e.z)
e = d >> rnd >> let(fun, a=5)  # Alternative syntax.
print(e.z)
"""
725.0
700000025.0
"""

# Output fields can be defined dynamically through parameter values.
# Input fields can be defined dynamically through kwargs.
copy = lambda source=None, target=None, **kwargs: {target: kwargs[source]}
d = empty >> {"x": 5}
d >>= let(copy, source="x", target="y")
print(d)
d.evaluate()
print(d)

"""
{
    "x": 5,
    "y": "→(source target x)"
}
{
    "x": 5,
    "y": 5
}
"""

Composition of sets of functions

from random import Random

from ldict import empty


# A multistep process can be defined without applying its functions


def g(x, y, a=[1, 2, 3, ..., 10], b=[0.00001, 0.0001, 0.001, ..., 100000]):
    return {"z": a * x + b * y}


def h(z, c=[1, 2, 3]):
    return {"z": c * z}


# In the ldict framework 'data is function',
# so the alias ø represents the 'empty data object' and the 'reflexive function' at the same time.
# In other words: 'inserting nothing' has the same effect as 'doing nothing'.
fun = empty >> g >> h  # empty enable the cartesian product of the subsequent sets of functions within the expression.
print(fun)
"""
«λ{} × λ»
"""

# An unnapplied function has its free parameters unsampled.
# A compostition of functions results in an ordered set (Cartesian product of sets).
# It is a set because the parameter values of the functions are still undefined.
d = {"x": 5, "y": 7} >> (Random(0) >> fun)
print(d)
"""
{
    "x": 5,
    "y": 7,
    "z": "→(c z→(a b x y))"
}
"""

print(d.z)
"""
105.0
"""

d = {"x": 5, "y": 7} >> (Random(0) >> fun)
print(d.z)
"""
105.0
"""

# Reproducible different runs by passing a stateful random number generator.
rnd = Random(0)
e = d >> rnd >> fun
print(e.z)
"""
105.0
"""

e = d >> rnd >> fun
print(e.z)
"""
14050.0
"""

# Repeating the same results.
rnd = Random(0)
e = d >> rnd >> fun
print(e.z)
"""
105.0
"""

e = d >> rnd >> fun
print(e.z)
"""
14050.0
"""

Concept

A ldict is like a common Python dict, with extra functionality and lazy. It is a mapping between string keys, called fields, and any serializable (pickable protocol=5) object.

Grants

This work was partially supported by Fapesp under supervision of Prof. André C. P. L. F. de Carvalho at CEPID-CeMEAI (Grants 2013/07375-0 – 2019/01735-0).