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"""Provides some utilities widely used by other modules"""
import
bisect
import
collections
import
collections
.
abc
import
heapq
import
operator
import
os
.
path
import
random
import
math
import
functools
import
numpy
as
np
from
itertools
import
chain
,
combinations
# ______________________________________________________________________________
# Functions on Sequences and Iterables
def
sequence
(
iterable
):
"""Converts iterable to sequence, if it is not already one."""
return
(
iterable
if
isinstance
(
iterable
,
collections
.
abc
.
Sequence
)
else
tuple
([
iterable
]))
def
removeall
(
item
,
seq
):
"""Return a copy of seq (or string) with all occurrences of item removed."""
if
isinstance
(
seq
,
str
):
return
seq
.
replace
(
item
,
''
)
else
:
return
[
x
for
x
in
seq
if
x
!=
item
]
def
unique
(
seq
):
"""Remove duplicate elements from seq. Assumes hashable elements."""
return
list
(
set
(
seq
))
def
count
(
seq
):
"""Count the number of items in sequence that are interpreted as true."""
return
sum
(
map
(
bool
,
seq
))
def
multimap
(
items
):
"""Given (key, val) pairs, return {key: [val, ....], ...}."""
result
=
collections
.
defaultdict
(
list
)
for
(
key
,
val
)
in
items
:
result
[
key
].
append
(
val
)
return
dict
(
result
)
def
multimap_items
(
mmap
):
"""Yield all (key, val) pairs stored in the multimap."""
for
(
key
,
vals
)
in
mmap
.
items
():
for
val
in
vals
:
yield
key
,
val
def
product
(
numbers
):
"""Return the product of the numbers, e.g. product([2, 3, 10]) == 60"""
result
=
1
for
x
in
numbers
:
result
*=
x
return
result
def
first
(
iterable
,
default
=
None
):
"""Return the first element of an iterable; or default."""
return
next
(
iter
(
iterable
),
default
)
def
is_in
(
elt
,
seq
):
"""Similar to (elt in seq), but compares with 'is', not '=='."""
return
any
(
x
is
elt
for
x
in
seq
)
def
mode
(
data
):
"""Return the most common data item. If there are ties, return any one of them."""
[(
item
,
count
)]
=
collections
.
Counter
(
data
).
most_common
(
1
)
return
item
def
powerset
(
iterable
):
"""powerset([1,2,3]) --> (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"""
s
=
list
(
iterable
)
return
list
(
chain
.
from_iterable
(
combinations
(
s
,
r
)
for
r
in
range
(
len
(
s
)
+
1
)))[
1
:]
# ______________________________________________________________________________
# argmin and argmax
identity
=
lambda
x
:
x
argmin
=
min
argmax
=
max
def
argmin_random_tie
(
seq
,
key
=
identity
):
"""Return a minimum element of seq; break ties at random."""
return
argmin
(
shuffled
(
seq
),
key
=
key
)
def
argmax_random_tie
(
seq
,
key
=
identity
):
"""Return an element with highest fn(seq[i]) score; break ties at random."""
return
argmax
(
shuffled
(
seq
),
key
=
key
)
def
shuffled
(
iterable
):
"""Randomly shuffle a copy of iterable."""
items
=
list
(
iterable
)
random
.
shuffle
(
items
)
return
items
# ______________________________________________________________________________
# Statistical and mathematical functions
def
histogram
(
values
,
mode
=
0
,
bin_function
=
None
):
"""Return a list of (value, count) pairs, summarizing the input values.
Sorted by increasing value, or if mode=1, by decreasing count.
If bin_function is given, map it over values first."""
if
bin_function
:
values
=
map
(
bin_function
,
values
)
bins
=
{}
for
val
in
values
:
bins
[
val
]
=
bins
.
get
(
val
,
0
)
+
1
if
mode
:
return
sorted
(
list
(
bins
.
items
()),
key
=
lambda
x
: (
x
[
1
],
x
[
0
]),
reverse
=
True
)
else
:
return
sorted
(
bins
.
items
())
def
dotproduct
(
X
,
Y
):
"""Return the sum of the element-wise product of vectors X and Y."""
return
sum
(
x
*
y
for
x
,
y
in
zip
(
X
,
Y
))
def
element_wise_product
(
X
,
Y
):
"""Return vector as an element-wise product of vectors X and Y"""
assert
len
(
X
)
==
len
(
Y
)
return
[
x
*
y
for
x
,
y
in
zip
(
X
,
Y
)]
def
matrix_multiplication
(
X_M
,
*
Y_M
):
"""Return a matrix as a matrix-multiplication of X_M and arbitrary number of matrices *Y_M"""
def
_mat_mult
(
X_M
,
Y_M
):
"""Return a matrix as a matrix-multiplication of two matrices X_M and Y_M
>>> matrix_multiplication([[1, 2, 3],
[2, 3, 4]],
[[3, 4],
[1, 2],
[1, 0]])
[[8, 8],[13, 14]]
"""
assert
len
(
X_M
[
0
])
==
len
(
Y_M
)
result
=
[[
0
for
i
in
range
(
len
(
Y_M
[
0
]))]
for
j
in
range
(
len
(
X_M
))]
for
i
in
range
(
len
(
X_M
)):
for
j
in
range
(
len
(
Y_M
[
0
])):
for
k
in
range
(
len
(
Y_M
)):
result
[
i
][
j
]
+=
X_M
[
i
][
k
]
*
Y_M
[
k
][
j
]
return
result
result
=
X_M
for
Y
in
Y_M
:
result
=
_mat_mult
(
result
,
Y
)
return
result
def
vector_to_diagonal
(
v
):
"""Converts a vector to a diagonal matrix with vector elements
as the diagonal elements of the matrix"""
diag_matrix
=
[[
0
for
i
in
range
(
len
(
v
))]
for
j
in
range
(
len
(
v
))]
for
i
in
range
(
len
(
v
)):
diag_matrix
[
i
][
i
]
=
v
[
i
]
return
diag_matrix
def
vector_add
(
a
,
b
):
"""Component-wise addition of two vectors."""
return
tuple
(
map
(
operator
.
add
,
a
,
b
))
def
scalar_vector_product
(
X
,
Y
):
"""Return vector as a product of a scalar and a vector"""
return
[
X
*
y
for
y
in
Y
]
def
scalar_matrix_product
(
X
,
Y
):
"""Return matrix as a product of a scalar and a matrix"""
return
[
scalar_vector_product
(
X
,
y
)
for
y
in
Y
]
def
inverse_matrix
(
X
):
"""Inverse a given square matrix of size 2x2"""
assert
len
(
X
)
==
2
assert
len
(
X
[
0
])
==
2
det
=
X
[
0
][
0
]
*
X
[
1
][
1
]
-
X
[
0
][
1
]
*
X
[
1
][
0
]
assert
det
!=
0
inv_mat
=
scalar_matrix_product
(
1.0
/
det
, [[
X
[
1
][
1
],
-
X
[
0
][
1
]], [
-
X
[
1
][
0
],
X
[
0
][
0
]]])
return
inv_mat
def
probability
(
p
):
"""Return true with probability p."""
return
p
>
random
.
uniform
(
0.0
,
1.0
)
def
weighted_sample_with_replacement
(
n
,
seq
,
weights
):
"""Pick n samples from seq at random, with replacement, with the
probability of each element in proportion to its corresponding
weight."""
sample
=
weighted_sampler
(
seq
,
weights
)
return
[
sample
()
for
_
in
range
(
n
)]
def
weighted_sampler
(
seq
,
weights
):
"""Return a random-sample function that picks from seq weighted by weights."""
totals
=
[]
for
w
in
weights
:
totals
.
append
(
w
+
totals
[
-
1
]
if
totals
else
w
)
return
lambda
:
seq
[
bisect
.
bisect
(
totals
,
random
.
uniform
(
0
,
totals
[
-
1
]))]
def
weighted_choice
(
choices
):
"""A weighted version of random.choice"""
# NOTE: Shoule be replaced by random.choices if we port to Python 3.6
total
=
sum
(
w
for
_
,
w
in
choices
)
r
=
random
.
uniform
(
0
,
total
)
upto
=
0
for
c
,
w
in
choices
:
if
upto
+
w
>=
r
:
return
c
,
w
upto
+=
w
def
rounder
(
numbers
,
d
=
4
):
"""Round a single number, or sequence of numbers, to d decimal places."""
if
isinstance
(
numbers
, (
int
,
float
)):
return
round
(
numbers
,
d
)
else
:
constructor
=
type
(
numbers
)
# Can be list, set, tuple, etc.
return
constructor
(
rounder
(
n
,
d
)
for
n
in
numbers
)
def
num_or_str
(
x
):
# TODO: rename as `atom`
"""The argument is a string; convert to a number if
possible, or strip it."""
try
:
return
int
(
x
)
except
ValueError
:
try
:
return
float
(
x
)
except
ValueError
:
return
str
(
x
).
strip
()
def
normalize
(
dist
):
"""Multiply each number by a constant such that the sum is 1.0"""
if
isinstance
(
dist
,
dict
):
total
=
sum
(
dist
.
values
())
for
key
in
dist
:
dist
[
key
]
=
dist
[
key
]
/
total
assert
0
<=
dist
[
key
]
<=
1
,
"Probabilities must be between 0 and 1."
return
dist
total
=
sum
(
dist
)
return
[(
n
/
total
)
for
n
in
dist
]
def
norm
(
X
,
n
=
2
):
"""Return the n-norm of vector X"""
return
sum
([
x
**
n
for
x
in
X
])
**
(
1
/
n
)
def
clip
(
x
,
lowest
,
highest
):
"""Return x clipped to the range [lowest..highest]."""
return
max
(
lowest
,
min
(
x
,
highest
))
def
sigmoid_derivative
(
value
):
return
value
*
(
1
-
value
)
def
sigmoid
(
x
):
"""Return activation value of x with sigmoid function"""
return
1
/
(
1
+
math
.
exp
(
-
x
))
def
relu_derivative
(
value
):
if
value
>
0
:
return
1
else
:
return
0
def
elu
(
x
,
alpha
=
0.01
):
if
x
>
0
:
return
x
else
:
return
alpha
*
(
math
.
exp
(
x
)
-
1
)
def
elu_derivative
(
value
,
alpha
=
0.01
):
if
value
>
0
:
return
1
else
:
return
alpha
*
math
.
exp
(
value
)
def
tanh
(
x
):
return
np
.
tanh
(
x
)
def
tanh_derivative
(
value
):
return
(
1
-
(
value
**
2
))
def
leaky_relu
(
x
,
alpha
=
0.01
):
if
x
>
0
:
return
x
else
:
return
alpha
*
x
def
leaky_relu_derivative
(
value
,
alpha
=
0.01
):
if
value
>
0
:
return
1
else
:
return
alpha
def
relu
(
x
):
return
max
(
0
,
x
)
def
relu_derivative
(
value
):
if
value
>
0
:
return
1
else
:
return
0
def
step
(
x
):
"""Return activation value of x with sign function"""
return
1
if
x
>=
0
else
0
def
gaussian
(
mean
,
st_dev
,
x
):
"""Given the mean and standard deviation of a distribution, it returns the probability of x."""
return
1
/
(
math
.
sqrt
(
2
*
math
.
pi
)
*
st_dev
)
*
math
.
e
**
(
-
0.5
*
(
float
(
x
-
mean
)
/
st_dev
)
**
2
)
try
:
# math.isclose was added in Python 3.5; but we might be in 3.4
from
math
import
isclose
except
ImportError
:
def
isclose
(
a
,
b
,
rel_tol
=
1e-09
,
abs_tol
=
0.0
):
"""Return true if numbers a and b are close to each other."""
return
abs
(
a
-
b
)
<=
max
(
rel_tol
*
max
(
abs
(
a
),
abs
(
b
)),
abs_tol
)
# ______________________________________________________________________________
# Grid Functions
orientations
=
EAST
,
NORTH
,
WEST
,
SOUTH
=
[(
1
,
0
), (
0
,
1
), (
-
1
,
0
), (
0
,
-
1
)]
turns
=
LEFT
,
RIGHT
=
(
+
1
,
-
1
)
def
turn_heading
(
heading
,
inc
,
headings
=
orientations
):
return
headings
[(
headings
.
index
(
heading
)
+
inc
)
%
len
(
headings
)]
def
turn_right
(
heading
):
return
turn_heading
(
heading
,
RIGHT
)
def
turn_left
(
heading
):
return
turn_heading
(
heading
,
LEFT
)
def
distance
(
a
,
b
):
"""The distance between two (x, y) points."""
xA
,
yA
=
a
xB
,
yB
=
b
return
math
.
hypot
((
xA
-
xB
), (
yA
-
yB
))
def
distance_squared
(
a
,
b
):
"""The square of the distance between two (x, y) points."""
xA
,
yA
=
a
xB
,
yB
=
b
return
(
xA
-
xB
)
**
2
+
(
yA
-
yB
)
**
2
def
vector_clip
(
vector
,
lowest
,
highest
):
"""Return vector, except if any element is less than the corresponding
value of lowest or more than the corresponding value of highest, clip to
those values."""
return
type
(
vector
)(
map
(
clip
,
vector
,
lowest
,
highest
))
# ______________________________________________________________________________
# Misc Functions
class
injection
():
"""Dependency injection of temporary values for global functions/classes/etc.
E.g., `with injection(DataBase=MockDataBase): ...`"""
def
__init__
(
self
,
**
kwds
):
self
.
new
=
kwds
def
__enter__
(
self
):
self
.
old
=
{
v
:
globals
()[
v
]
for
v
in
self
.
new
}
globals
().
update
(
self
.
new
)
def
__exit__
(
self
,
type
,
value
,
traceback
):
globals
().
update
(
self
.
old
)
def
memoize
(
fn
,
slot
=
None
,
maxsize
=
32
):
"""Memoize fn: make it remember the computed value for any argument list.
If slot is specified, store result in that slot of first argument.
If slot is false, use lru_cache for caching the values."""
if
slot
:
def
memoized_fn
(
obj
,
*
args
):
if
hasattr
(
obj
,
slot
):
return
getattr
(
obj
,
slot
)
else
:
val
=
fn
(
obj
,
*
args
)
setattr
(
obj
,
slot
,
val
)
return
val
else
:
@
functools
.
lru_cache
(
maxsize
=
maxsize
)
def
memoized_fn
(
*
args
):
return
fn
(
*
args
)
return
memoized_fn
def
name
(
obj
):
"""Try to find some reasonable name for the object."""
return
(
getattr
(
obj
,
'name'
,
0
)
or
getattr
(
obj
,
'__name__'
,
0
)
or
getattr
(
getattr
(
obj
,
'__class__'
,
0
),
'__name__'
,
0
)
or
str
(
obj
))
def
isnumber
(
x
):
"""Is x a number?"""
return
hasattr
(
x
,
'__int__'
)
def
issequence
(
x
):
"""Is x a sequence?"""
return
isinstance
(
x
,
collections
.
abc
.
Sequence
)
def
print_table
(
table
,
header
=
None
,
sep
=
' '
,
numfmt
=
'{}'
):
"""Print a list of lists as a table, so that columns line up nicely.
header, if specified, will be printed as the first row.
numfmt is the format for all numbers; you might want e.g. '{:.2f}'.
(If you want different formats in different columns,
don't use print_table.) sep is the separator between columns."""
justs
=
[
'rjust'
if
isnumber
(
x
)
else
'ljust'
for
x
in
table
[
0
]]
if
header
:
table
.
insert
(
0
,
header
)
table
=
[[
numfmt
.
format
(
x
)
if
isnumber
(
x
)
else
x
for
x
in
row
]
for
row
in
table
]
sizes
=
list
(
map
(
lambda
seq
:
max
(
map
(
len
,
seq
)),
list
(
zip
(
*
[
map
(
str
,
row
)
for
row
in
table
]))))
for
row
in
table
:
print
(
sep
.
join
(
getattr
(
str
(
x
),
j
)(
size
)
for
(
j
,
size
,
x
)
in
zip
(
justs
,
sizes
,
row
)))
def
open_data
(
name
,
mode
=
'r'
):
aima_root
=
os
.
path
.
dirname
(
__file__
)
aima_file
=
os
.
path
.
join
(
aima_root
,
*
[
'aima-data'
,
name
])
return
open
(
aima_file
,
mode
=
mode
)
def
failure_test
(
algorithm
,
tests
):
"""Grades the given algorithm based on how many tests it passes.
Most algorithms have arbitrary output on correct execution, which is difficult
to check for correctness. On the other hand, a lot of algorithms output something
particular on fail (for example, False, or None).
tests is a list with each element in the form: (values, failure_output)."""
from
statistics
import
mean
return
mean
(
int
(
algorithm
(
x
)
!=
y
)
for
x
,
y
in
tests
)
# ______________________________________________________________________________
# Expressions
# See https://docs.python.org/3/reference/expressions.html#operator-precedence
# See https://docs.python.org/3/reference/datamodel.html#special-method-names
class
Expr
(
object
):
"""A mathematical expression with an operator and 0 or more arguments.
op is a str like '+' or 'sin'; args are Expressions.
Expr('x') or Symbol('x') creates a symbol (a nullary Expr).
Expr('-', x) creates a unary; Expr('+', x, 1) creates a binary."""
def
__init__
(
self
,
op
,
*
args
):
self
.
op
=
str
(
op
)
self
.
args
=
args
# Operator overloads
def
__neg__
(
self
):
return
Expr
(
'-'
,
self
)
def
__pos__
(
self
):
return
Expr
(
'+'
,
self
)
def
__invert__
(
self
):
return
Expr
(
'~'
,
self
)
def
__add__
(
self
,
rhs
):
return
Expr
(
'+'
,
self
,
rhs
)
def
__sub__
(
self
,
rhs
):
return
Expr
(
'-'
,
self
,
rhs
)
def
__mul__
(
self
,
rhs
):
return
Expr
(
'*'
,
self
,
rhs
)
def
__pow__
(
self
,
rhs
):
return
Expr
(
'**'
,
self
,
rhs
)
def
__mod__
(
self
,
rhs
):
return
Expr
(
'%'
,
self
,
rhs
)
def
__and__
(
self
,
rhs
):
return
Expr
(
'&'
,
self
,
rhs
)
def
__xor__
(
self
,
rhs
):
return
Expr
(
'^'
,
self
,
rhs
)
def
__rshift__
(
self
,
rhs
):
return
Expr
(
'>>'
,
self
,
rhs
)
def
__lshift__
(
self
,
rhs
):
return
Expr
(
'<<'
,
self
,
rhs
)
def
__truediv__
(
self
,
rhs
):
return
Expr
(
'/'
,
self
,
rhs
)
def
__floordiv__
(
self
,
rhs
):
return
Expr
(
'//'
,
self
,
rhs
)
def
__matmul__
(
self
,
rhs
):
return
Expr
(
'@'
,
self
,
rhs
)
def
__or__
(
self
,
rhs
):
"""Allow both P | Q, and P |'==>'| Q."""
if
isinstance
(
rhs
,
Expression
):
return
Expr
(
'|'
,
self
,
rhs
)
else
:
return
PartialExpr
(
rhs
,
self
)
# Reverse operator overloads
def
__radd__
(
self
,
lhs
):
return
Expr
(
'+'
,
lhs
,
self
)
def
__rsub__
(
self
,
lhs
):
return
Expr
(
'-'
,
lhs
,
self
)
def
__rmul__
(
self
,
lhs
):
return
Expr
(
'*'
,
lhs
,
self
)
def
__rdiv__
(
self
,
lhs
):
return
Expr
(
'/'
,
lhs
,
self
)
def
__rpow__
(
self
,
lhs
):
return
Expr
(
'**'
,
lhs
,
self
)
def
__rmod__
(
self
,
lhs
):
return
Expr
(
'%'
,
lhs
,
self
)
def
__rand__
(
self
,
lhs
):
return
Expr
(
'&'
,
lhs
,
self
)
def
__rxor__
(
self
,
lhs
):
return
Expr
(
'^'
,
lhs
,
self
)
def
__ror__
(
self
,
lhs
):
return
Expr
(
'|'
,
lhs
,
self
)
def
__rrshift__
(
self
,
lhs
):
return
Expr
(
'>>'
,
lhs
,
self
)
def
__rlshift__
(
self
,
lhs
):
return
Expr
(
'<<'
,
lhs
,
self
)
def
__rtruediv__
(
self
,
lhs
):
return
Expr
(
'/'
,
lhs
,
self
)
def
__rfloordiv__
(
self
,
lhs
):
return
Expr
(
'//'
,
lhs
,
self
)
def
__rmatmul__
(
self
,
lhs
):
return
Expr
(
'@'
,
lhs
,
self
)
def
__call__
(
self
,
*
args
):
"Call: if 'f' is a Symbol, then f(0) == Expr('f', 0)."
if
self
.
args
:
raise
ValueError
(
'can only do a call for a Symbol, not an Expr'
)
else
:
return
Expr
(
self
.
op
,
*
args
)
# Equality and repr
def
__eq__
(
self
,
other
):
"'x == y' evaluates to True or False; does not build an Expr."
return
(
isinstance
(
other
,
Expr
)
and
self
.
op
==
other
.
op
and
self
.
args
==
other
.
args
)
def
__hash__
(
self
):
return
hash
(
self
.
op
)
^
hash
(
self
.
args
)
def
__repr__
(
self
):
op
=
self
.
op
args
=
[
str
(
arg
)
for
arg
in
self
.
args
]
if
op
.
isidentifier
():
# f(x) or f(x, y)
return
'{}({})'
.
format
(
op
,
', '
.
join
(
args
))
if
args
else
op
elif
len
(
args
)
==
1
:
# -x or -(x + 1)
return
op
+
args
[
0
]
else
:
# (x - y)
opp
=
(
' '
+
op
+
' '
)
return
'('
+
opp
.
join
(
args
)
+
')'
# An 'Expression' is either an Expr or a Number.
# Symbol is not an explicit type; it is any Expr with 0 args.
Number
=
(
int
,
float
,
complex
)
Expression
=
(
Expr
,
Number
)
def
Symbol
(
name
):
"""A Symbol is just an Expr with no args."""
return
Expr
(
name
)
def
symbols
(
names
):
"""Return a tuple of Symbols; names is a comma/whitespace delimited str."""
return
tuple
(
Symbol
(
name
)
for
name
in
names
.
replace
(
','
,
' '
).
split
())
def
subexpressions
(
x
):
"""Yield the subexpressions of an Expression (including x itself)."""
yield
x
if
isinstance
(
x
,
Expr
):
for
arg
in
x
.
args
:
yield
from
subexpressions
(
arg
)
def
arity
(
expression
):
"""The number of sub-expressions in this expression."""
if
isinstance
(
expression
,
Expr
):
return
len
(
expression
.
args
)
else
:
# expression is a number
return
0
# For operators that are not defined in Python, we allow new InfixOps:
class
PartialExpr
:
"""Given 'P |'==>'| Q, first form PartialExpr('==>', P), then combine with Q."""
def
__init__
(
self
,
op
,
lhs
):
self
.
op
,
self
.
lhs
=
op
,
lhs
def
__or__
(
self
,
rhs
):
return
Expr
(
self
.
op
,
self
.
lhs
,
rhs
)
def
__repr__
(
self
):
return
"PartialExpr('{}', {})"
.
format
(
self
.
op
,
self
.
lhs
)
def
expr
(
x
):
"""Shortcut to create an Expression. x is a str in which:
- identifiers are automatically defined as Symbols.
- ==> is treated as an infix |'==>'|, as are <== and <=>.
If x is already an Expression, it is returned unchanged. Example:
>>> expr('P & Q ==> Q')
((P & Q) ==> Q)
"""
if
isinstance
(
x
,
str
):
return
eval
(
expr_handle_infix_ops
(
x
),
defaultkeydict
(
Symbol
))
else
:
return
x
infix_ops
=
'==> <== <=>'
.
split
()
def
expr_handle_infix_ops
(
x
):
"""Given a str, return a new str with ==> replaced by |'==>'|, etc.
>>> expr_handle_infix_ops('P ==> Q')
"P |'==>'| Q"
"""
for
op
in
infix_ops
:
x
=
x
.
replace
(
op
,
'|'
+
repr
(
op
)
+
'|'
)
return
x
class
defaultkeydict
(
collections
.
defaultdict
):
"""Like defaultdict, but the default_factory is a function of the key.
>>> d = defaultkeydict(len); d['four']
4
"""
def
__missing__
(
self
,
key
):
self
[
key
]
=
result
=
self
.
default_factory
(
key
)
return
result
class
hashabledict
(
dict
):
"""Allows hashing by representing a dictionary as tuple of key:value pairs
May cause problems as the hash value may change during runtime
"""
def
__hash__
(
self
):
return
1
# ______________________________________________________________________________
# Queues: Stack, FIFOQueue, PriorityQueue
# Stack and FIFOQueue are implemented as list and collection.deque
# PriorityQueue is implemented here
class
PriorityQueue
:
"""A Queue in which the minimum (or maximum) element (as determined by f and
order) is returned first.
If order is 'min', the item with minimum f(x) is
returned first; if order is 'max', then it is the item with maximum f(x).
Also supports dict-like lookup."""
def
__init__
(
self
,
order
=
'min'
,
f
=
lambda
x
:
x
):
self
.
heap
=
[]
if
order
==
'min'
:
self
.
f
=
f
elif
order
==
'max'
:
# now item with max f(x)
self
.
f
=
lambda
x
:
-
f
(
x
)
# will be popped first
else
:
raise
ValueError
(
"order must be either 'min' or 'max'."
)
def
append
(
self
,
item
):
"""Insert item at its correct position."""
heapq
.
heappush
(
self
.
heap
, (
self
.
f
(
item
),
item
))
def
extend
(
self
,
items
):
"""Insert each item in items at its correct position."""
for
item
in
items
:
self
.
append
(
item
)
def
pop
(
self
):
"""Pop and return the item (with min or max f(x) value)
depending on the order."""
if
self
.
heap
:
return
heapq
.
heappop
(
self
.
heap
)[
1
]
else
:
raise
Exception
(
'Trying to pop from empty PriorityQueue.'
)
def
__len__
(
self
):
"""Return current capacity of PriorityQueue."""
return
len
(
self
.
heap
)
def
__contains__
(
self
,
item
):
"""Return True if item in PriorityQueue."""
return
(
self
.
f
(
item
),
item
)
in
self
.
heap
def
__getitem__
(
self
,
key
):
for
_
,
item
in
self
.
heap
:
if
item
==
key
:
return
item
def
__delitem__
(
self
,
key
):
"""Delete the first occurrence of key."""
self
.
heap
.
remove
((
self
.
f
(
key
),
key
))
heapq
.
heapify
(
self
.
heap
)
# ______________________________________________________________________________
# Useful Shorthands
class
Bool
(
int
):
"""Just like `bool`, except values display as 'T' and 'F' instead of 'True' and 'False'"""
__str__
=
__repr__
=
lambda
self
:
'T'
if
self
else
'F'
T
=
Bool
(
True
)
F
=
Bool
(
False
)
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