Phi is a library for fluent functional programming in Python which includes a DSL + facilities to create libraries that integrate with it.

## Project Description

# Phi

Phi library for functional programming in Python that intends to remove as much of the pain as possible from your functional programming experience in Python.

## Import

For demonstration purposes we will import right now everything we will need for the rest of the exercises like this

```python

from phi.api import *

```

but you can also import just what you need from the `phi` module.

## Math-like Lambdas

#### Operators

Using the `P` object you can create quick lambdas using any operator. You can write things like

```python

f = (P * 6) / (P + 2) #lambda x: (x * 6) / (x + 2)

assert f(2) == 3 # (2 * 6) / (2 + 2) == 12 / 4 == 3

```

where the expression for `f` is equivalent to

```python

f = lambda x: (x * 6) / (x + 2)

```

#### getitem

You can also use the `P` object to create lambdas that access the items of a collection

```python

f = P[0] + P[-1] #lambda x: x[0] + x[-1]

assert f([1,2,3,4]) == 5 #1 + 4 == 5

```

#### field access

If you want create lambdas that access the field of some entity you can use the `Rec` (for Record) object an call that field on it

```python

from collections import namedtuple

Point = namedtuple('Point', ['x', 'y'])

f = Rec.x + Rec.y #lambda p: p.x + p.y

assert f(Point(3, 4)) == 7 #point.x + point.y == 3 + 4 == 7

```

#### method calling

If you want to create a lambda that calls the method of an object you use the `Obj` object and call that method on it with the parameters

```python

f = Obj.upper() + ", " + Obj.lower() #lambda s: s.upper() + ", " + s.lower()

assert f("HEllo") == "HELLO, hello" # "HEllo".upper() + ", " + "HEllo".lower() == "HELLO" + ", " + "hello" == "HELLO, hello"

```

Here no parameters were needed but in general

```python

f = Obj.some_method(arg1, arg2, ...) #lambda obj: obj.some_method(arg1, arg2, ...)

```

is equivalent to

```python

f = lambda obj: obj.some_method(arg1, arg2, ...)

```

## Composition

#### >> and <<

You can use the `>>` operator to *forward* compose expressions

```python

f = P + 7 >> math.sqrt #executes left to right

assert f(2) == 3 # math.sqrt(2 + 7) == math.sqrt(9) == 3

```

This is preferred because it is more readable, but you can use the `<<` to compose them *backwards* just like the mathematical definition of function composition

```python

f = math.sqrt << P + 7 #executes right to left

assert f(2) == 3 # math.sqrt(2 + 7) == math.sqrt(9) == 3

```

#### Seq and Pipe

If you need to do a long or complex composition you can use `Seq` (for 'Sequence') instead of many chained `>>`

```python

f = Seq(

str,

P + "00",

int,

math.sqrt

)

assert f(1) == 10 # sqrt(int("1" + "00")) == sqrt(100) == 10

```

If you want to create a composition and directly apply it to an initial value you can use `Pipe`

```python

assert 10 == Pipe(

1, #input

str, # "1"

P + "00", # "1" + "00" == "100"

int, # 100

math.sqrt #sqrt(100) == 10

)

```

## Combinators

#### List, Tuple, Set, Dict

There are a couple of combinators like `List`, `Tuple`, `Set`, `Dict` that help you create compound functions that return the container types `list`, `tuple`, `set` and `dict` respectively. For example, you can pass `List` a couple of expressions to get a function that returns a list with the values of these functions

```python

f = List( P + 1, P * 10 ) #lambda x: [ x +1, x * 10 ]

assert f(3) == [ 4, 30 ] # [ 3 + 1, 3 * 10 ] == [ 4, 30 ]

```

The same logic applies for `Tuple` and `Set`. With `Dict` you have to use keyword arguments

```python

f = Dict( x = P + 1, y = P * 10 ) #lambda x: [ x +1, x * 10 ]

d = f(3)

assert d == { 'x': 4, 'y': 30 } # { 'x': 3 + 1, 'y': 3 * 10 } == { 'x': 4, 'y': 30 }

assert d.x == 4 #access d['x'] via field access as d.x

assert d.y == 30 #access d['y'] via field access as d.y

```

As you see, `Dict` returns a custom `dict` that also allows *field access*, this is useful because you can use it in combination with `Rec`.

#### State: Read and Write

Internally all these expressions are implemented in such a way that they not only pass their computed values but also pass a **state** dictionary between them in a functional manner. By reading from and writing to this state dictionary the `Read` and `Write` combinators can help you "save" the state of intermediate computations to read them later

```python

assert [70, 30] == Pipe(

3,

Write(s = P * 10), #s = 3 * 10 == 30

P + 5, #30 + 5 == 35

List(

P * 2 # 35 * 2 == 70

,

Read('s') #s == 30

)

)

```

If you need to perform many reads inside a list -usually for output- you can use `ReadList` instead

```python

assert [2, 4, 22] == Pipe(

1,

Write(a = P + 1), #a = 1 + 1 == 2

Write(b = P * 2), #b = 2 * 2 == 4

P * 5, # 4 * 5 == 20

ReadList('a', 'b', P + 2) # [a, b, 20 + 2] == [2, 4, 22]

)

```

`ReadList` interprets string elements as `Read`s, so the previous is translated to

```python

List(Read('a'), Read('b'), P + 2)

```

#### Then, Then2, ..., Then5, ThenAt

To create a partial expression from a function e.g.

```python

def repeat_word(word, times, upper=False):

if upper:

word = word.upper()

return [ word ] * times

```

use the `Then` combinator which accepts a function plus all but the *1st* of its `*args` + `**kwargs`

```python

f = P[::-1] >> Then(repeat_word, 3)

g = P[::-1] >> Then(repeat_word, 3, upper=True)

assert f("ward") == ["draw", "draw", "draw"]

assert g("ward") == ["DRAW", "DRAW", "DRAW"]

```

and assumes that the *1st* argument of the function will be applied last, e.g. `word` in the case of `repeat_word`. If you need the *2nd* argument to be applied last use `Then2`, and so on. In general you can use `ThenAt(n, f, *args, **kwargs)` where `n` is the position of the argument that will be applied last. Example

```python

# since map and filter receive the iterable on their second argument, you have to use `Then2`

f = Then2(filter, P % 2 == 0) >> Then2(map, P**2) >> list #lambda x: map(lambda z: z**2, filter(lambda z: z % 2 == 0, x))

assert f([1,2,3,4,5]) == [4, 16] #[2**2, 4**2] == [4, 16]

```

Be aware that `P` already has the `map` and `filter` methods so you can write the previous more easily as

```python

f = P.filter(P % 2 == 0) >> P.map(P**2) >> list #lambda x: map(lambda z: z**2, filter(lambda z: z % 2 == 0, x))

assert f([1,2,3,4,5]) == [4, 16] #[2**2, 4**2] == [4, 16]

```

#### Val

If you need to create a constant function with a given value use `Val`

```python

f = Val(42) #lambda x: 42

assert f("whatever") == 42

```

#### Others

Check out the `With`, `If` and more, combinators on the documentation. The `P` object also offers some useful combinators as methods such as `Not`, `First`, `Last` plus **almost all** python built in functions as methods:

```python

f = Obj.split(' ') >> P.map(len) >> sum >> If( (P < 15).Not(), "Great! Got {0} letters!".format).Else("Too short, need at-least 15 letters")

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

## The DSL

Phi has a small omnipresent DSL that has these simple rules:

1. Any element of the class `Expression` is an element of the DSL. `P` and all the combinators are of the `Expression` class.

2. Any callable of arity 1 is an element of the DSL.

3. The container types `list`, `tuple`, `set`, and `dict` are elements of the DSL. They are translated to their counterparts `List`, `Tuple`, `Set` and `Dict`, their internal elements are forwarded.

4. Any value `x` that does not comply with any of the previous rules is also an element of the DSL and is translated to `Val(x)`.

Using the DSL, the expression

```python

f = P**2 >> List( P, Val(3), Val(4) ) #lambda x: [ x**2]

assert f(10) == [ 100, 3, 4 ] # [ 10**2, 3, 4 ] == [ 100, 3, 4 ]

```

can be rewritten as

```python

f = P**2 >> [ P, 3, 4 ]

assert f(10) == [ 100, 3, 4 ] # [ 10 ** 2, 3, 4 ] == [ 100, 3, 4 ]

```

Here the values `3` and `4` are translated to `Val(3)` and `Val(4)` thanks to the *4th* rule, and `[...]` is translated to `List(...)` thanks to the *3rd* rule. Since the DSL is omnipresent you can use it inside any core function, so the previous can be rewritten using `Pipe` as

```python

assert [ 100, 3, 4 ] == Pipe(

10,

P**2, # 10**2 == 100

[ P, 3, 4 ] #[ 100, 3, 4 ]

)

```

#### F

You can *compile* any element to an `Expression` using `F`

```python

f = F((P + "!!!", 42, Obj.upper())) #Tuple(P + "!!!", Val(42), Obj.upper())

assert f("some tuple") == ("some tuple!!!", 42, "SOME TUPLE")

```

Other example

```python

f = F([ P + n for n in range(5) ]) >> [ len, sum ] # lambda x: [ len([ x, x+1, x+2, x+3, x+4]), sum([ x, x+1, x+2, x+3, x+4]) ]

assert f(10) == [ 5, 60 ] # [ len([10, 11, 12, 13, 14]), sum([10, 11, 12, 13, 14])] == [ 5, (50 + 0 + 1 + 2 + 3 + 4) ] == [ 5, 60 ]

```

## Fluent Programming

All the functions you've seen are ultimately methods of the `PythonBuilder` class which inherits from the `Expression`, therefore you can also [fluently](https://en.wikipedia.org/wiki/Fluent_interface) chain methods instead of using the `>>` operator. For example

```python

f = Dict(

x = 2 * P,

y = P + 1

).Tuple(

Rec.x + Rec.y,

Rec.y / Rec.x

)

assert f(1) == (4, 1) # ( x + y, y / x) == ( 2 + 2, 2 / 2) == ( 4, 1 )

```

This more complicated previous example

```python

f = Obj.split(' ') >> P.map(len) >> sum >> If( (P < 15).Not(), "Great! Got {0} letters!".format).Else("Too short, need at-least 15 letters")

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

can be be rewritten as

```python

f = (

Obj.split(' ')

.map(len)

.sum()

.If( (P < 15).Not(),

"Great! Got {0} letters!".format

).Else(

"Too short, need at-least 15 letters"

)

)

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

## Integrability

#### Register, Register2, ..., Register5, RegistarAt

If you want to have custom expressions to deal with certain data types, you can create a custom class that inherits from `Builder` or `PythonBuilder`

```python

from phi import PythonBuilder

class MyBuilder(PythonBuilder):

pass

M = MyBuilder()

```

and register your function in it using the `Register` class method

```python

def remove_longer_than(some_list, n):

return [ elem from elem in some_list if len(elem) <= n ]

MyBuilder.Register(remove_longer_than, "my.lib.")

```

Or better even use `Register` as a decorator

```python

@MyBuilder.Register("my.lib.")

def remove_longer_than(some_list, n):

return [ elem for elem in some_list if len(elem) <= n ]

```

Now the method `MyBuilder.remove_longer_than` exists on this class. You can then use it like this

```python

f = Obj.lower() >> Obj.split(' ') >> M.remove_longer_than(6)

assert f("SoMe aRe LONGGGGGGGGG") == ["some", "are"]

```

As you see the argument `n = 6` was partially applied to `remove_longer_than`, an expression which waits for the `some_list` argument to be returned. Internally the `Registar*` method family uses the `Then*` method family.

#### PatchAt

If you want to register a batch of functions from a module or class automatically you can use the `PatchAt` class method. It's an easy way to integrate an entire module to Phi's DSL. See `PatchAt`.

#### Libraries

Phi currently powers the following libraries that integrate with its DSL:

* [PythonBuilder](https://cgarciae.github.io/phi/python_builder.m.html) : helps you integrate Python's built-in functions and keywords into the phi DSL and it also includes a bunch of useful helpers for common stuff. `phi`'s global `P` object is an instance of this class. [Shipped with Phi]

* [TensorBuilder](https://github.com/cgarciae/tensorbuilder): a TensorFlow library enables you to easily create complex deep neural networks by leveraging the phi DSL to help define their structure.

* NumpyBuilder: Comming soon!

## Documentation

Check out the [complete documentation](https://cgarciae.github.io/phi/).

## More Examples

The global `phi.P` object exposes most of the API and preferably should be imported directly. The most simple thing the DSL does is function composition:

```python

from phi.api import *

def add1(x): return x + 1

def mul3(x): return x * 3

x = Pipe(

1.0, #input 1

add1, #1 + 1 == 2

mul3 #2 * 3 == 6

)

assert x == 6

```

Use phi [lambdas](https://cgarciae.github.io/phi/lambdas.m.html) to create the functions

```python

from phi.api import *

x = Pipe(

1.0, #input 1

P + 1, #1 + 1 == 2

P * 3 #2 * 3 == 6

)

assert x == 6

```

Create a branched computation instead

```python

from phi.api import *

[x, y] = Pipe(

1.0, #input 1

[

P + 1 #1 + 1 == 2

,

P * 3 #1 * 3 == 3

]

)

assert x == 2

assert y == 3

```

Compose it with a function equivalent to `f(x) = (x + 3) / (x + 1)`

```python

from phi.api import *

[x, y] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

[

P + 1 #2 + 1 == 3

,

P * 3 #2 * 3 == 6

]

)

assert x == 3

assert y == 6

```

Give names to the branches

```python

from phi.api import *

result = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

)

)

assert result.x == 3

assert result.y == 6

```

Divide `x` by `y`.

```python

from phi.api import *

result = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

Rec.x / Rec.y #3 / 6 == 0.5

)

assert result == 0.5

```

Save the value from the `(P + 3) / (P + 1)` computation as `s` and load it at the end in a branch

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

Write(s = (P + 3) / (P + 1)), #s = 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read('s') #s == 2

]

)

assert result == 0.5

assert s == 2

```

Add 3 to the loaded `s` for fun and profit

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

Write(s = (P + 3) / (P + 1)), #s = 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read('s') + 3 # 2 + 3 == 5

]

)

assert result == 0.5

assert s == 5

```

Use the `Read` and `Write` field access lambda style just because

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #4 / 2 == 2

Write.s, #s = 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

]

)

assert result == 0.5

assert s == 5

```

Add an input `Val` of 9 on a branch and add to it 1 just for the sake of it

```python

from phi.api import *

[result, s, val] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

Val(9) + 1 #input 9 and add 1, gives 10

]

)

assert result == 0.5

assert s == 5

assert val == 10

```

Do the previous only if `y > 7` else return `"Sorry, come back latter."`

```python

from phi.api import *

[result, s, val] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

If( Rec.y > 7,

Val(9) + 1 #input 9 and add 1, gives 10

).Else(

"Sorry, come back latter."

)

]

)

assert result == 0.5

assert s == 5

assert val == "Sorry, come back latter."

```

Now, what you have to understand that everything you've done with these expression is to create and apply a single function. Using `Seq` we can get the standalone function and then use it to get the same values as before

```python

from phi.api import *

f = Seq(

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

If( Rec.y > 7,

Val(9) + 1 #input 9 and add 1, gives 10

).Else(

"Sorry, come back latter."

)

]

)

[result, s, val] = f(1.0)

assert result == 0.5

assert s == 5

assert val == "Sorry, come back latter."

```

### Even More Examples

```python

from phi.api import *

avg_word_length = Pipe(

"1 22 333",

Obj.split(" "), # ['1', '22', '333']

P.map(len), # [1, 2, 3]

P.sum() / P.len() # sum([1,2,3]) / len([1,2,3]) == 6 / 3 == 2

)

assert 2 == avg_word_length

```

```python

from phi.api import *

assert False == Pipe(

[1,2,3,4], P

.filter(P % 2 != 0) #[1, 3], keeps odds

.Contains(4) #4 in [1, 3] == False

)

```

```python

from phi.api import *

assert {'a': 97, 'b': 98, 'c': 99} == Pipe(

"a b c", Obj

.split(' ').Write.keys # keys = ['a', 'b', 'c']

.map(ord), # [ord('a'), ord('b'), ord('c')] == [97, 98, 99]

lambda it: zip(Ref.keys, it), # [('a', 97), ('b', 98), ('c', 99)]

dict # {'a': 97, 'b': 98, 'c': 99}

)

```

## Installation

pip install phi

#### Bleeding Edge

pip install git+https://github.com/cgarciae/phi.git@develop

## Status

* Version: **0.6.4**.

* Documentation coverage: 100%. Please create an issue if documentation is unclear, it is a high priority of this library.

* Milestone: reach 1.0.0 after feedback from the community.

Phi library for functional programming in Python that intends to remove as much of the pain as possible from your functional programming experience in Python.

## Import

For demonstration purposes we will import right now everything we will need for the rest of the exercises like this

```python

from phi.api import *

```

but you can also import just what you need from the `phi` module.

## Math-like Lambdas

#### Operators

Using the `P` object you can create quick lambdas using any operator. You can write things like

```python

f = (P * 6) / (P + 2) #lambda x: (x * 6) / (x + 2)

assert f(2) == 3 # (2 * 6) / (2 + 2) == 12 / 4 == 3

```

where the expression for `f` is equivalent to

```python

f = lambda x: (x * 6) / (x + 2)

```

#### getitem

You can also use the `P` object to create lambdas that access the items of a collection

```python

f = P[0] + P[-1] #lambda x: x[0] + x[-1]

assert f([1,2,3,4]) == 5 #1 + 4 == 5

```

#### field access

If you want create lambdas that access the field of some entity you can use the `Rec` (for Record) object an call that field on it

```python

from collections import namedtuple

Point = namedtuple('Point', ['x', 'y'])

f = Rec.x + Rec.y #lambda p: p.x + p.y

assert f(Point(3, 4)) == 7 #point.x + point.y == 3 + 4 == 7

```

#### method calling

If you want to create a lambda that calls the method of an object you use the `Obj` object and call that method on it with the parameters

```python

f = Obj.upper() + ", " + Obj.lower() #lambda s: s.upper() + ", " + s.lower()

assert f("HEllo") == "HELLO, hello" # "HEllo".upper() + ", " + "HEllo".lower() == "HELLO" + ", " + "hello" == "HELLO, hello"

```

Here no parameters were needed but in general

```python

f = Obj.some_method(arg1, arg2, ...) #lambda obj: obj.some_method(arg1, arg2, ...)

```

is equivalent to

```python

f = lambda obj: obj.some_method(arg1, arg2, ...)

```

## Composition

#### >> and <<

You can use the `>>` operator to *forward* compose expressions

```python

f = P + 7 >> math.sqrt #executes left to right

assert f(2) == 3 # math.sqrt(2 + 7) == math.sqrt(9) == 3

```

This is preferred because it is more readable, but you can use the `<<` to compose them *backwards* just like the mathematical definition of function composition

```python

f = math.sqrt << P + 7 #executes right to left

assert f(2) == 3 # math.sqrt(2 + 7) == math.sqrt(9) == 3

```

#### Seq and Pipe

If you need to do a long or complex composition you can use `Seq` (for 'Sequence') instead of many chained `>>`

```python

f = Seq(

str,

P + "00",

int,

math.sqrt

)

assert f(1) == 10 # sqrt(int("1" + "00")) == sqrt(100) == 10

```

If you want to create a composition and directly apply it to an initial value you can use `Pipe`

```python

assert 10 == Pipe(

1, #input

str, # "1"

P + "00", # "1" + "00" == "100"

int, # 100

math.sqrt #sqrt(100) == 10

)

```

## Combinators

#### List, Tuple, Set, Dict

There are a couple of combinators like `List`, `Tuple`, `Set`, `Dict` that help you create compound functions that return the container types `list`, `tuple`, `set` and `dict` respectively. For example, you can pass `List` a couple of expressions to get a function that returns a list with the values of these functions

```python

f = List( P + 1, P * 10 ) #lambda x: [ x +1, x * 10 ]

assert f(3) == [ 4, 30 ] # [ 3 + 1, 3 * 10 ] == [ 4, 30 ]

```

The same logic applies for `Tuple` and `Set`. With `Dict` you have to use keyword arguments

```python

f = Dict( x = P + 1, y = P * 10 ) #lambda x: [ x +1, x * 10 ]

d = f(3)

assert d == { 'x': 4, 'y': 30 } # { 'x': 3 + 1, 'y': 3 * 10 } == { 'x': 4, 'y': 30 }

assert d.x == 4 #access d['x'] via field access as d.x

assert d.y == 30 #access d['y'] via field access as d.y

```

As you see, `Dict` returns a custom `dict` that also allows *field access*, this is useful because you can use it in combination with `Rec`.

#### State: Read and Write

Internally all these expressions are implemented in such a way that they not only pass their computed values but also pass a **state** dictionary between them in a functional manner. By reading from and writing to this state dictionary the `Read` and `Write` combinators can help you "save" the state of intermediate computations to read them later

```python

assert [70, 30] == Pipe(

3,

Write(s = P * 10), #s = 3 * 10 == 30

P + 5, #30 + 5 == 35

List(

P * 2 # 35 * 2 == 70

,

Read('s') #s == 30

)

)

```

If you need to perform many reads inside a list -usually for output- you can use `ReadList` instead

```python

assert [2, 4, 22] == Pipe(

1,

Write(a = P + 1), #a = 1 + 1 == 2

Write(b = P * 2), #b = 2 * 2 == 4

P * 5, # 4 * 5 == 20

ReadList('a', 'b', P + 2) # [a, b, 20 + 2] == [2, 4, 22]

)

```

`ReadList` interprets string elements as `Read`s, so the previous is translated to

```python

List(Read('a'), Read('b'), P + 2)

```

#### Then, Then2, ..., Then5, ThenAt

To create a partial expression from a function e.g.

```python

def repeat_word(word, times, upper=False):

if upper:

word = word.upper()

return [ word ] * times

```

use the `Then` combinator which accepts a function plus all but the *1st* of its `*args` + `**kwargs`

```python

f = P[::-1] >> Then(repeat_word, 3)

g = P[::-1] >> Then(repeat_word, 3, upper=True)

assert f("ward") == ["draw", "draw", "draw"]

assert g("ward") == ["DRAW", "DRAW", "DRAW"]

```

and assumes that the *1st* argument of the function will be applied last, e.g. `word` in the case of `repeat_word`. If you need the *2nd* argument to be applied last use `Then2`, and so on. In general you can use `ThenAt(n, f, *args, **kwargs)` where `n` is the position of the argument that will be applied last. Example

```python

# since map and filter receive the iterable on their second argument, you have to use `Then2`

f = Then2(filter, P % 2 == 0) >> Then2(map, P**2) >> list #lambda x: map(lambda z: z**2, filter(lambda z: z % 2 == 0, x))

assert f([1,2,3,4,5]) == [4, 16] #[2**2, 4**2] == [4, 16]

```

Be aware that `P` already has the `map` and `filter` methods so you can write the previous more easily as

```python

f = P.filter(P % 2 == 0) >> P.map(P**2) >> list #lambda x: map(lambda z: z**2, filter(lambda z: z % 2 == 0, x))

assert f([1,2,3,4,5]) == [4, 16] #[2**2, 4**2] == [4, 16]

```

#### Val

If you need to create a constant function with a given value use `Val`

```python

f = Val(42) #lambda x: 42

assert f("whatever") == 42

```

#### Others

Check out the `With`, `If` and more, combinators on the documentation. The `P` object also offers some useful combinators as methods such as `Not`, `First`, `Last` plus **almost all** python built in functions as methods:

```python

f = Obj.split(' ') >> P.map(len) >> sum >> If( (P < 15).Not(), "Great! Got {0} letters!".format).Else("Too short, need at-least 15 letters")

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

## The DSL

Phi has a small omnipresent DSL that has these simple rules:

1. Any element of the class `Expression` is an element of the DSL. `P` and all the combinators are of the `Expression` class.

2. Any callable of arity 1 is an element of the DSL.

3. The container types `list`, `tuple`, `set`, and `dict` are elements of the DSL. They are translated to their counterparts `List`, `Tuple`, `Set` and `Dict`, their internal elements are forwarded.

4. Any value `x` that does not comply with any of the previous rules is also an element of the DSL and is translated to `Val(x)`.

Using the DSL, the expression

```python

f = P**2 >> List( P, Val(3), Val(4) ) #lambda x: [ x**2]

assert f(10) == [ 100, 3, 4 ] # [ 10**2, 3, 4 ] == [ 100, 3, 4 ]

```

can be rewritten as

```python

f = P**2 >> [ P, 3, 4 ]

assert f(10) == [ 100, 3, 4 ] # [ 10 ** 2, 3, 4 ] == [ 100, 3, 4 ]

```

Here the values `3` and `4` are translated to `Val(3)` and `Val(4)` thanks to the *4th* rule, and `[...]` is translated to `List(...)` thanks to the *3rd* rule. Since the DSL is omnipresent you can use it inside any core function, so the previous can be rewritten using `Pipe` as

```python

assert [ 100, 3, 4 ] == Pipe(

10,

P**2, # 10**2 == 100

[ P, 3, 4 ] #[ 100, 3, 4 ]

)

```

#### F

You can *compile* any element to an `Expression` using `F`

```python

f = F((P + "!!!", 42, Obj.upper())) #Tuple(P + "!!!", Val(42), Obj.upper())

assert f("some tuple") == ("some tuple!!!", 42, "SOME TUPLE")

```

Other example

```python

f = F([ P + n for n in range(5) ]) >> [ len, sum ] # lambda x: [ len([ x, x+1, x+2, x+3, x+4]), sum([ x, x+1, x+2, x+3, x+4]) ]

assert f(10) == [ 5, 60 ] # [ len([10, 11, 12, 13, 14]), sum([10, 11, 12, 13, 14])] == [ 5, (50 + 0 + 1 + 2 + 3 + 4) ] == [ 5, 60 ]

```

## Fluent Programming

All the functions you've seen are ultimately methods of the `PythonBuilder` class which inherits from the `Expression`, therefore you can also [fluently](https://en.wikipedia.org/wiki/Fluent_interface) chain methods instead of using the `>>` operator. For example

```python

f = Dict(

x = 2 * P,

y = P + 1

).Tuple(

Rec.x + Rec.y,

Rec.y / Rec.x

)

assert f(1) == (4, 1) # ( x + y, y / x) == ( 2 + 2, 2 / 2) == ( 4, 1 )

```

This more complicated previous example

```python

f = Obj.split(' ') >> P.map(len) >> sum >> If( (P < 15).Not(), "Great! Got {0} letters!".format).Else("Too short, need at-least 15 letters")

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

can be be rewritten as

```python

f = (

Obj.split(' ')

.map(len)

.sum()

.If( (P < 15).Not(),

"Great! Got {0} letters!".format

).Else(

"Too short, need at-least 15 letters"

)

)

assert f("short frase") == "Too short, need at-least 15 letters"

assert f("some longer frase") == "Great! Got 15 letters!"

```

## Integrability

#### Register, Register2, ..., Register5, RegistarAt

If you want to have custom expressions to deal with certain data types, you can create a custom class that inherits from `Builder` or `PythonBuilder`

```python

from phi import PythonBuilder

class MyBuilder(PythonBuilder):

pass

M = MyBuilder()

```

and register your function in it using the `Register` class method

```python

def remove_longer_than(some_list, n):

return [ elem from elem in some_list if len(elem) <= n ]

MyBuilder.Register(remove_longer_than, "my.lib.")

```

Or better even use `Register` as a decorator

```python

@MyBuilder.Register("my.lib.")

def remove_longer_than(some_list, n):

return [ elem for elem in some_list if len(elem) <= n ]

```

Now the method `MyBuilder.remove_longer_than` exists on this class. You can then use it like this

```python

f = Obj.lower() >> Obj.split(' ') >> M.remove_longer_than(6)

assert f("SoMe aRe LONGGGGGGGGG") == ["some", "are"]

```

As you see the argument `n = 6` was partially applied to `remove_longer_than`, an expression which waits for the `some_list` argument to be returned. Internally the `Registar*` method family uses the `Then*` method family.

#### PatchAt

If you want to register a batch of functions from a module or class automatically you can use the `PatchAt` class method. It's an easy way to integrate an entire module to Phi's DSL. See `PatchAt`.

#### Libraries

Phi currently powers the following libraries that integrate with its DSL:

* [PythonBuilder](https://cgarciae.github.io/phi/python_builder.m.html) : helps you integrate Python's built-in functions and keywords into the phi DSL and it also includes a bunch of useful helpers for common stuff. `phi`'s global `P` object is an instance of this class. [Shipped with Phi]

* [TensorBuilder](https://github.com/cgarciae/tensorbuilder): a TensorFlow library enables you to easily create complex deep neural networks by leveraging the phi DSL to help define their structure.

* NumpyBuilder: Comming soon!

## Documentation

Check out the [complete documentation](https://cgarciae.github.io/phi/).

## More Examples

The global `phi.P` object exposes most of the API and preferably should be imported directly. The most simple thing the DSL does is function composition:

```python

from phi.api import *

def add1(x): return x + 1

def mul3(x): return x * 3

x = Pipe(

1.0, #input 1

add1, #1 + 1 == 2

mul3 #2 * 3 == 6

)

assert x == 6

```

Use phi [lambdas](https://cgarciae.github.io/phi/lambdas.m.html) to create the functions

```python

from phi.api import *

x = Pipe(

1.0, #input 1

P + 1, #1 + 1 == 2

P * 3 #2 * 3 == 6

)

assert x == 6

```

Create a branched computation instead

```python

from phi.api import *

[x, y] = Pipe(

1.0, #input 1

[

P + 1 #1 + 1 == 2

,

P * 3 #1 * 3 == 3

]

)

assert x == 2

assert y == 3

```

Compose it with a function equivalent to `f(x) = (x + 3) / (x + 1)`

```python

from phi.api import *

[x, y] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

[

P + 1 #2 + 1 == 3

,

P * 3 #2 * 3 == 6

]

)

assert x == 3

assert y == 6

```

Give names to the branches

```python

from phi.api import *

result = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

)

)

assert result.x == 3

assert result.y == 6

```

Divide `x` by `y`.

```python

from phi.api import *

result = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #(1 + 3) / (1 + 1) == 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

Rec.x / Rec.y #3 / 6 == 0.5

)

assert result == 0.5

```

Save the value from the `(P + 3) / (P + 1)` computation as `s` and load it at the end in a branch

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

Write(s = (P + 3) / (P + 1)), #s = 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read('s') #s == 2

]

)

assert result == 0.5

assert s == 2

```

Add 3 to the loaded `s` for fun and profit

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

Write(s = (P + 3) / (P + 1)), #s = 4 / 2 == 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read('s') + 3 # 2 + 3 == 5

]

)

assert result == 0.5

assert s == 5

```

Use the `Read` and `Write` field access lambda style just because

```python

from phi.api import *

[result, s] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), #4 / 2 == 2

Write.s, #s = 2

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

]

)

assert result == 0.5

assert s == 5

```

Add an input `Val` of 9 on a branch and add to it 1 just for the sake of it

```python

from phi.api import *

[result, s, val] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

Val(9) + 1 #input 9 and add 1, gives 10

]

)

assert result == 0.5

assert s == 5

assert val == 10

```

Do the previous only if `y > 7` else return `"Sorry, come back latter."`

```python

from phi.api import *

[result, s, val] = Pipe(

1.0, #input 1

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

If( Rec.y > 7,

Val(9) + 1 #input 9 and add 1, gives 10

).Else(

"Sorry, come back latter."

)

]

)

assert result == 0.5

assert s == 5

assert val == "Sorry, come back latter."

```

Now, what you have to understand that everything you've done with these expression is to create and apply a single function. Using `Seq` we can get the standalone function and then use it to get the same values as before

```python

from phi.api import *

f = Seq(

(P + 3) / (P + 1), Write.s, #4 / 2 == 2, saved as 's'

dict(

x = P + 1 #2 + 1 == 3

,

y = P * 3 #2 * 3 == 6

),

[

Rec.x / Rec.y #3 / 6 == 0.5

,

Read.s + 3 # 2 + 3 == 5

,

If( Rec.y > 7,

Val(9) + 1 #input 9 and add 1, gives 10

).Else(

"Sorry, come back latter."

)

]

)

[result, s, val] = f(1.0)

assert result == 0.5

assert s == 5

assert val == "Sorry, come back latter."

```

### Even More Examples

```python

from phi.api import *

avg_word_length = Pipe(

"1 22 333",

Obj.split(" "), # ['1', '22', '333']

P.map(len), # [1, 2, 3]

P.sum() / P.len() # sum([1,2,3]) / len([1,2,3]) == 6 / 3 == 2

)

assert 2 == avg_word_length

```

```python

from phi.api import *

assert False == Pipe(

[1,2,3,4], P

.filter(P % 2 != 0) #[1, 3], keeps odds

.Contains(4) #4 in [1, 3] == False

)

```

```python

from phi.api import *

assert {'a': 97, 'b': 98, 'c': 99} == Pipe(

"a b c", Obj

.split(' ').Write.keys # keys = ['a', 'b', 'c']

.map(ord), # [ord('a'), ord('b'), ord('c')] == [97, 98, 99]

lambda it: zip(Ref.keys, it), # [('a', 97), ('b', 98), ('c', 99)]

dict # {'a': 97, 'b': 98, 'c': 99}

)

```

## Installation

pip install phi

#### Bleeding Edge

pip install git+https://github.com/cgarciae/phi.git@develop

## Status

* Version: **0.6.4**.

* Documentation coverage: 100%. Please create an issue if documentation is unclear, it is a high priority of this library.

* Milestone: reach 1.0.0 after feedback from the community.

## Release History

## Download Files

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