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Relations are now frozen

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Salvo 'LtWorf' Tomaselli 2020-08-13 11:04:22 +02:00
parent 87ec732d24
commit 4722c9b0e8
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1 changed files with 27 additions and 56 deletions
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relational/relation.py
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@ -20,7 +20,7 @@
# relational operations on them.
import csv
from itertools import chain, repeat
from itertools import chain, repeat, product as iproduct
from collections import deque
from typing import *
from pathlib import Path
@ -66,7 +66,7 @@ class Relation(NamedTuple):
reader = csv.reader(fp) # Creating a csv reader
header = Header(next(reader)) # read 1st line
#FIXME load properly
content = frozenset((tuple(i) for i in reader))
content = frozenset((tuple(Rstring(s) for s in i) for i in reader))
return Relation(header, content)
def __iter__(self):
@ -111,14 +111,14 @@ class Relation(NamedTuple):
'''
Selection, expr must be a valid Python expression; can contain field names.
'''
newt = Relation()
newt.header = Header(self.header)
header = Header(self.header)
try:
c_expr = compile(expr, 'selection', 'eval')
except:
raise Exception('Failed to compile expression: %s' % expr)
content = set()
for i in self.content:
# Fills the attributes dictionary with the values of the tuple
attributes = {attr: i[j].autocast()
@ -127,11 +127,11 @@ class Relation(NamedTuple):
try:
if eval(c_expr, attributes):
newt.content.add(i)
content.add(i)
except Exception as e:
raise Exception(
"Failed to evaluate %s\n%s" % (expr, e.__str__()))
return newt
return Relation(header, frozenset(content))
def product(self, other: 'Relation') -> 'Relation':
'''
@ -144,13 +144,10 @@ class Relation(NamedTuple):
raise Exception(
'Unable to perform product on relations with colliding attributes'
)
newt = Relation()
newt.header = Header(self.header + other.header)
header = Header(self.header + other.header)
for i in self.content:
for j in other.content:
newt.content.add(i + j)
return newt
content = frozenset(i+j for i, j in iproduct(self.content, other.content))
return Relation(header, content)
def projection(self, *attributes) -> 'Relation':
'''
@ -172,16 +169,11 @@ class Relation(NamedTuple):
if len(ids) == 0:
raise Exception('Invalid attributes for projection')
newt = Relation()
# Create the header
h = (self.header[i] for i in ids)
newt.header = Header(h)
header = Header((self.header[i] for i in ids))
# Create the body
for i in self.content:
row = (i[j] for j in ids)
newt.content.add(tuple(row))
return newt
content = frozenset(tuple((i[j] for j in ids)) for i in self.content)
return Relation(header, content)
def rename(self, params: Dict[str, str]) -> 'Relation':
'''
@ -192,12 +184,8 @@ class Relation(NamedTuple):
For example if you want to rename a to b, call
rel.rename({'a':'b'})
'''
newt = Relation()
newt.header = self.header.rename(params)
newt.content = self.content
self._make_duplicate(newt)
return newt
header = self.header.rename(params)
return Relation(header, self.content)
def intersection(self, other: 'Relation') -> 'Relation':
'''
@ -206,22 +194,14 @@ class Relation(NamedTuple):
Will return an empty one if there are no common items.
'''
other = self._rearrange(other) # Rearranges attributes' order
newt = Relation()
newt.header = Header(self.header)
newt.content = self.content.intersection(other.content)
return newt
return Relation(self.header, self.content.intersection(other.content))
def difference(self, other: 'Relation') -> 'Relation':
'''Difference operation. The result will contain items present in first
operand but not in second one.
'''
other = self._rearrange(other) # Rearranges attributes' order
newt = Relation()
newt.header = Header(self.header)
newt.content = self.content.difference(other.content)
return newt
return Relation(self.header, self.content.difference(other.content))
def division(self, other: 'Relation') -> 'Relation':
'''Division operator
@ -254,11 +234,7 @@ class Relation(NamedTuple):
and second operands.
'''
other = self._rearrange(other) # Rearranges attributes' order
newt = Relation()
newt.header = Header(self.header)
newt.content = self.content.union(other.content)
return newt
return Relation(self.header, self.content.union(other.content))
def thetajoin(self, other: 'Relation', expr: str) -> 'Relation':
'''Defined as product and then selection with the given expression.'''
@ -288,11 +264,10 @@ class Relation(NamedTuple):
shared = self.header.intersection(other.header)
newt = Relation() # Creates the new relation
# Creating the header with all the fields, done like that because order is
# needed
h = (i for i in other.header if i not in shared)
newt.header = Header(chain(self.header, h))
header = Header(chain(self.header, h))
# Shared ids of self
sid = self.header.getAttributesId(shared)
@ -302,6 +277,7 @@ class Relation(NamedTuple):
# Non shared ids of the other relation
noid = [i for i in range(len(other.header)) if i not in oid]
content = set()
for i in self.content:
# Tuple partecipated to the join?
added = False
@ -313,14 +289,14 @@ class Relation(NamedTuple):
if match:
item = chain(i, (j[l] for l in noid))
newt.content.add(tuple(item))
content.add(tuple(item))
added = True
# If it didn't partecipate, adds it
if not added:
item = chain(i, repeat(Rstring('---'), len(noid)))
newt.content.add(tuple(item))
content.add(tuple(item))
return newt
return Relation(header, frozenset(content))
def join(self, other: 'Relation') -> 'Relation':
'''
@ -331,12 +307,10 @@ class Relation(NamedTuple):
# List of attributes in common between the relations
shared = self.header.intersection(other.header)
newt = Relation() # Creates the new relation
# Creating the header with all the fields, done like that because order is
# needed
h = (i for i in other.header if i not in shared)
newt.header = Header(chain(self.header, h))
header = Header(chain(self.header, h))
# Shared ids of self
sid = self.header.getAttributesId(shared)
@ -346,6 +320,7 @@ class Relation(NamedTuple):
# Non shared ids of the other relation
noid = [i for i in range(len(other.header)) if i not in oid]
content = set()
for i in self.content:
for j in other.content:
match = True
@ -354,9 +329,9 @@ class Relation(NamedTuple):
if match:
item = chain(i, (j[l] for l in noid))
newt.content.add(tuple(item))
content.add(tuple(item))
return newt
return Relation(header, frozenset(content))
def __eq__(self, other):
if not isinstance(other, Relation):
@ -410,7 +385,6 @@ class Relation(NamedTuple):
Returns the number of affected rows.
'''
self._make_writable(copy_content=False)
affected = self.selection(expr)
not_affected = self.difference(affected)
@ -446,8 +420,6 @@ class Relation(NamedTuple):
)
)
self._make_writable()
prevlen = len(self.content)
self.content.add(tuple(map(Rstring, values)))
return len(self.content) - prevlen
@ -462,7 +434,6 @@ class Relation(NamedTuple):
Returns the number of affected rows.'''
l = len(self.content)
self._make_writable(copy_content=False)
self.content = self.difference(self.selection(expr)).content
return len(self.content) - l