Compatibility

Added by Sean McKay

Some basic compatibility:

namespace Boo.Compatibility.Python
class Dict(Hash):
    def constructor():
        super()
    def constructor(h as Hash):
        super()
        Update(h)
    def Update(h as Hash):
        for key in h.Keys:
            self[key] = h[key]
    def Get(key, default):
        return self[key] or default
    def SetDefault(key, default):
        if self.Contains(key):
            return self[key]
        else:
            self[key] = default
            return default

Recipe 1.1: Swap values without a temporary variable:

a = 4
b = 5
c = 6

//DIFF FROM PYTHON ---> print is a fxn, although can be a macro
//Use print macro.., no ending comma
print a, b, c

a, b, c = b, c, a		

print a, b, c

Recipe 1.2: Construct a Dictionary without excessive quoting

/*Recipe welcome

data = {'red':1, 'green':2, 'blue':3}  #"excessive quoting"
data = makedict((red=1, green=2, blue=3)) //Gives warnings about unused variables
print data["red"]
*/

Recipe 1.3: Getting a Value safely from a Dictionary

d = {'key':'value'}

//DIFF FROM PYTHON ---> Contains or ContainsKey instead of has_key
if d.Contains('key'): 
	print d['key']
else:
	print('not found')

//DIFF FROM PYTHON ---> No get with a default value.
#print(d.get('key', 'not found'))
//Boo equivalent because not found hashes return null
print d['key'] or 'not found'

//DIFF FROM PYTHON ---> No nested fxns

Recipe 1.4: Adding an Entry to a Dictionary

def addword1(theIndex as Hash, word, pagenumber):
	// As of 1/7/05 , autocompletion doesn't work on theIndex in SharpDevelop
	if theIndex.ContainsKey(word): 
	//DIFF FROM Python ---> List instead of list
	//DIFF FROM Python ---> ArrayList value must be cast for compiler to work (1/7/05)
	//DIFF FROM PYTHON ---> Add function instead of append function.
		(theIndex[word] as List).Add(pagenumber) 
	else:
		theIndex[word] = [pagenumber]

#VERSUS
def addword2(theIndex as Hash, word, pagenumber):
	try: 
		(theIndex[word] as List).Add(pagenumber)
	except AttributeError: 
		theIndex[word] = [pagenumber]
	
//DIFF FROM Python ---> No setdefault.
#VERSUS
#def addword(theIndex as Hash, word, pagenumber):
#	theIndex.setdefault(word, []).append(pagenumber)
	
def wordcount(theIndex as Hash,word):
	//theIndex[word] = 1 + theIndex.get(word, 0)
	i as int= (theIndex[word] or 0)
	theIndex[word] = 1 + i

theIndex = {}

addword1(theIndex, "keys", 1)
addword2(theIndex, "job", 2)
//DIFF FROM Python ---> Hash instead of dict
//DIFF FROM Python ---> Able to declare types of variables.

Recipe 1.5:Associating Multiple Values with Each Key in a Dictionary

//Recipe 1.5:Associating Multiple Values with Each Key in a Dictionary
key = "email"
value = "jbob@bob.net"

#Allows duplicates
d1 = {}
//d1.setdefault(key, []).append(value)
//NO SETDEFAULT
if not d1.ContainsKey(key): 
	d1[key] = []
(d1[key] as List).Add(value)

#Doesn't allow duplicates
d2 = {}
//d2.setdefault(key, {})[value] = 1
if not d2.ContainsKey(key): 
	d2[key] = {}
(d2[key] as Hash)[value] = 1
print d2[key]		

Recipe 1.6: Dispatching Using a Dictionary

//DIFFERENCE FROM PYTHON --> Referencing global or module variables not allowed.
//Globals class per Doug Holton feedback.
class Globals:
	public static number_of_felines = 0

def deal_with_a_cat(animals as List):
	print "meow"
	animals.Add("feline")
	Globals.number_of_felines +=1
	
def deal_with_a_dog(animals as List):
	print "bark"
	animals.Add("canine")
	
def deal_with_a_bear(animals as List):
	print "watch out for the *HUG*!"
	animals.Add("ursine")

animals = []
tokenDict = {
	"cat": deal_with_a_cat,
	"dog": deal_with_a_dog,
	"bear": deal_with_a_bear
	}
//Doesn't work in boo.. seems like dict (since it is a hash table) loses the type..
//Casting as callable is necessary to simulate the Python effect.
for word in ["cat", "bear", "cat", "dog"]:
	functionToCall = tokenDict[word] as callable
	functionToCall(animals)
	#Or
	(tokenDict[word] as callable)(animals)

Recipe 1.7 : Collecting a Bunch of Named Items

//Modified from Bill Woods Expando example at http://svn.boo.codehaus.org/boo/trunk/tests/testcases/integration/duck-5.boo?view=auto
import System

class Bunch(IQuackFu):

	_attributes = {}

	def constructor(attributes as Hash):
		self._attributes = attributes
	
	def QuackSet(name as string, value):
		_attributes[name] = value
		return value

	def QuackGet(name as string):
		raise "attribute not found: " + name  if not _attributes.Contains( name)
		return _attributes[name]
		
	def QuackInvoke(name as string, args as (object)) as object:
		pass
		
data = {'datum':2, 'squared':2*2, 'coord':5}
point as duck = Bunch(data)
print point.datum, point.squared, point.coord

if point.squared > 4:
	point.isok = true
else:
	point.isok = false
print point.isok		
*/

Recipe 1.8: Finding the Intersection of Two Dictionaries

#Bad way..
/*
def badslowway(some_dict as Hash, another_dict as Hash):
    intersect = []
    
    for item as string in some_dict.Keys:
        if item in another_dict.Keys:
            intersect.Add(item)
    return intersect
*/

#Better:
def simpleway(some_dict as Hash, another_dict as Hash):
    Globals.lastName = GetMethodName()    
    intersects = []
    for k as string in some_dict.Keys:
        if another_dict.Contains(k):
            intersects.Add(k)
    return intersects

#Using List Comprehension
def listcompway(some_dict as Hash, another_dict as Hash):
    Globals.lastName = GetMethodName()    
    return [k for k as string in some_dict.Keys if another_dict.Contains(k)]

#Using Filter
//def filterway(some_dict, another_dict):
//    return filter(another_dict.Contains, some_dict.Keys)

class Globals:
    public static some_dict = { 'zope':'zzz', 'boo':'rocks'}
    public static another_dict = { 'boo':'rocks', 'perl':'$'}
    public static lastName as string

def doNothing(a as Hash, b as Hash):
    Globals.lastName = GetMethodName()    
    return ''

def GetMethodName() as string:
    st = System.Diagnostics.StackTrace()
    sf as System.Diagnostics.StackFrame = st.GetFrame(1)
    return sf.GetMethod().Name

def time(fun as callable, n):
    //Determine fxn call overhead
    a = []
    start = System.DateTime.Now.Ticks
    for i in range(n):
        a.Add(doNothing(Globals.some_dict,Globals.another_dict))
    end = System.DateTime.Now.Ticks
    overhead = end-start
    a = []
    start = System.DateTime.Now.Ticks
    for i in range(n):
        a.Add(fun(Globals.some_dict,Globals.another_dict))
    end = System.DateTime.Now.Ticks
    duration = end-start-overhead
    print Globals.lastName,    System.TimeSpan.FromTicks(duration)


for f as callable in [simpleway,listcompway]: //,filterway,badslowway]:
    time(f,10000)

Recipe 1.9: Assigning and Testing with One Statement.

//In python the following isn't easy:
//If x=fxn():
//	doSomething()
//In boo, it is.  Remember == is the test for equality for boo.
def inc(x as int):
   return x + 1

if y = inc(5):
   print "Passed"
else:
   print "Failed"

//returns "Passed"

Recipe 1.10: Using List Comprehensions instead of map and filter.

//Differences:
//Python provides some builtins to do functional programming: map, filter.
//Boo provides only a map builtin.

//In any case, using list comprehensions is often a more readable approach.

def square(v as int):
	return v*v

print "Using map:"
results = map((1,3,5,6),square)
for r in results:
	print r

print "Using list comprehensions"
results = [square(x) for x in (1,3,5, 6)]
for r in results:
	print r

//list comprehensions can also filter the results in a way that map by itself can't (but python could using filter).
print "Return only the squares of evens"
results = [square(x) for x in (1,3,5,6) if x % 2 == 0]
for r in results:
	print r

Recipe 1.11: Unzipping Simple List Like Objects.

//A recipe to provide the unzip counterpart to the zip builtin.

/********************************************************************
Split a sequence p into a list of n tuples,
repeatedly taking next unused element of p and adding it to the next tuple.  
Each of the resulting tuples is of the same length; if p%n != 0, the shorter
tuples are padded with null (closer to the behavior of map than to that of zip-- 
in python at least.)
Example:
	>>> unzip(['a','b','c','d','e'],3)
	[('a','d'),('b','e'),('c',null)]
*********************************************************************/

def unzip(p as List, n as int) as List:
    //First, find the length for the longest sublist.
    lft as int
    mlen = System.Math.DivRem(p.Count, n, lft)
    if lft != 0:
        mlen +=1
    
    //Then, initialize a list of lists with suitable lengths
    lst as List = [[null]*mlen for i in range(n)]
    
    //Loop over all items of the input sequence (index-wise), and Copy
    // a reference to each into the appropriate place.
    k as int
    for i in range(p.Count):
        j = System.Math.DivRem(i, n, k)		//Find sublist-index and index-within-sublist
        (lst[k] as List)[j] = p[i]					//Copy a reference appropriately

    //Finally, turn each sublist into an array, since the unzip function
    //is specified to return a list of arrays, not a list of lists.
    return [array(val) for val in lst ]

x = unzip(['a','b','c','d','e'],3)
print x

Recipe 1.12: Flattening a nested sequence

import System.Collections

def flatten(sequence as List, isScalar as callable, result as List) as List:
	if result is null:
		result = []
	for item in sequence:
		if isScalar(item):
			result.Add(item)
		else:
			flatten(item,isScalar,result)
	return result

//Using Generators
def flattenWithGenerators(sequence as List, isScalar as callable) as object:
	for item in sequence:
		if isScalar(item):
			yield item
		else:
			for subitem in flattenWithGenerators(item as List,isScalar):
				yield subitem

//Checking if an item is loopable
def canLoopOver(item) as bool:
	ie = item as System.Collections.IEnumerable 
	return not ie is null

def isStringLike(obj) as bool:
	try:
		x = obj + ''
		return true
	except:
		return false

def isScalar(obj) as bool:
	return isStringLike(obj) or not canLoopOver(obj)

//Provided by Doug Holton:
//In boo you can do it like this:
def flatten2(seq as List):
       l = []
       for subseq as List in seq:
               l += subseq
       return l

//or a more general solution perhaps:

def flatten3(obj) as List:
       l = []
       if obj isa IEnumerable and not (obj isa string):
               for item in obj:
                       l += flatten3(item)
       else:
               l.Add(obj)
       return l

print flatten2([[0], [1,2,3], [4,5], [6,7,8,9], []]) //->[1,2,3,4,5,6,7,8,9]

print flatten3([[0], [1,2,3], [4,5], [6,7,8,9], []]) //->[1,2,3,4,5,6,7,8,9]
print flatten3(1) //-> [1]
print flatten3([[[[1]]],[2],3,[[4,5]]]) //-> [1,2,3,4,5]

y as List= [[1,2],2,3,[4,5]]
print flatten(y,isScalar,[])
print flattenWithGenerators(y,isScalar)

Recipe 1.13: Looping in Parallel over Index and Sequence Items

//Looping over a list and knowing the index of a particular item.
import System.Reflection

//This (A):
[DefaultMember("Item")]
class Indexed(List):
	seq as List
	def constructor(seq as List):
		self.seq = seq

	def Item():
		for idx in range(seq.Count):
			yield seq[idx],idx


def something(item, index):
	print "something + " + item +" + " + index

sequence = ["Cat", "Dog", "Elephant"]
indices = range(System.Int32.MaxValue)



//(A) Cont'd
//(A) Cont'd
for item, index in Indexed(sequence).Item():
	something(item, index)

//or this (B):
for item, index in zip(sequence, indices):
	something(item, index)
	
//is approximately equivalent to this (C):
for index in range(len(sequence)):
	something(sequence[index], index)

Recipe 1.14: Loop through every item of multiple lists

//To loop through multiple lists .. one element at a time..


def loop(a as List, b as List):
	for i in range(a.Count):
		if i < b.Count:
			yield (a[i], b[i])
		else:
			yield (a[i],null)




//data
a = ['a1','a2','a3']
b = ['b1','b2']

//Python map approach is not valid.

print "Zip:"
for x,y in zip(a,b):
	print x,y
print "3rd iteration: a3 is not done"

print "List Comprehension:"
for x,y in [(x,y) for x in a for y in b]:
	print x,y


print "Generators: Methods"
for x,y in loop(a,b):
	print x,y

print "Generators: Expressions"
for x,y in ((a[i],b[i]) for i in range(a.Count)):
	print x,y
//Exception at the last one.

Recipe 1.15 Spanning a Range Defined by Floats

def frange(start as double, end as double, inc as double):
//A range-like function that does accept float increments...
	assert inc>0, "Increment must be greater than 0."
	L = []
	while 1:
		next = start + len(L) * inc
		if next >=end:
			break
		L.Add(next)
		
	return L

def frange(start as double, inc as double):
	end = start
	start = 0.0
	return frange(start, end, inc)

def frange2(start as double, end as double, inc as double):
//A faster range-like function that does accept float increments..
	assert inc>0, "Increment must be greater than 0."
	count as int = (end-start) / inc
	if start + count * inc != end:
		//Need to adjust the count.  It comes up one short.
		count +=1
		
	L = [start] * count
	for i in range(1, count):
		L[i] = start + i * inc
		
	return L
	
	
def frange2(start as double, inc as double):
	end = start
	start = 0.0
	return frange2(start,end, inc)
	
def frangei(start as double, end as double, inc as double):
//A generator version of xrange that accepts floats
	assert inc>0, "Increment must be greater than 0."
	i = 0
	while 1:
		next = start + i * inc
		if next >= end:
			break
		yield next
		i+=1

def frangei(start as double, inc as double):
	end = start
	start = 0.0
	return frangei(start,end, inc)

			
print "frange: "
print frange(-5,5,1.7)
print "frange2: "
print frange2(-5,5,1.7)
print "frangei: "
print frangei(-5,5,1.7)

Recipe 1.16 Transposing Two-Dimensional Arrays

//Recipe 1.16 - Transposing Two-Dimensional Arrays
arr = [[1,2,3], [4,5,6],[7,8,9],[10,11,12]]

//Simple route: List comprehension:
x = [[r[col] for r as duck in arr] for col in range(len(arr[0]))]
print x

//or if one line matters:
print( [[r[col] for r as duck in arr] for col in range(len(arr[0]))])

Recipe 1.17 - Creating Lists of Lists Without Sharing References

//Dont use macro when first character is left-bracket.  Causes callable does not support slicing error.
print( [0]*5)  
multi = [[0] * 5]*3
print multi
i as List = multi[0]
i[0] = -999999
print multi  //Note that all 3 arrays had their first value changed!!

print string.Empty
//To prevent this:
//Use list comprehension:
multilist = [[0 for col in range(5)] for row in range(3)]
print multilist
i = multilist[0]
i[0] = -999999
print multilist //Note that the data is protected.