一入python深似海--dict(字典)的一种实现

以下是python中字典的一种实现。用list数据结构实现字典。详细是这种：[[(key1,value1),(key2,value2),...],[],[],...]

内部每个hash地址是一个list,存放hash地址同样的(key,value)对。

dict代码

def Map(num_buckets=256):
    """Initializes a Map with the given number of buckets."""
    aMap = []
    for i in range(0, num_buckets):
        aMap.append([])
    return aMap

def Map_hash(aMap, key):
    """Given a key this will create a number and then convert it to
    and index for the aMap's buckets."""
    return hash(key) % len(aMap)

def Map_get_bucket(aMap, key):
    """Given a key, find the bucket where it would go."""
    bucket_id = Map_hash(aMap, key)
    return aMap[bucket_id]

def Map_get_slot(aMap, key, default=None):
    """Returns the index, key, and value of a slot found in a bucket."""
    bucket = Map_get_bucket(aMap, key)

    for i, kv in enumerate(bucket):#bucket=[[k1,v1],[k2,v2],...]
        k, v = kv
        if key == k:
            return i, k, v#ex1:i=0,k=k1,v=v1

    return -1, key, default

def Map_get(aMap, key, default=None):
    """Gets the value in a bucket for the given key, or the default."""
    i, k, v = Map_get_slot(aMap, key, default=default)
    return v

def Map_set(aMap, key, value):
    """Sets the key to the value, replacing any existing value."""
    bucket = Map_get_bucket(aMap, key)
    i, k, v = Map_get_slot(aMap, key)

    if v:
        bucket[i] = (key, value)#key/value pair
    else:
        bucket.append((key, value))

def Map_delete(aMap, key):
    """Deletes the given key from the Map."""
    bucket = Map_get_bucket(aMap, key)

    for i in xrange(len(bucket)):
        k, v = bucket[i]
        if key == k:
            del bucket[i]
            break

def Map_list(aMap):
    """Prints out what's in the Map."""
    for bucket in aMap:
        if bucket:
            for k, v in bucket:
                print k, v

# The tests that it will work.

jazz = Map()
Map_set(jazz, 'Miles Davis', 'Flamenco Sketches')
# confirms set will replace previous one
Map_set(jazz, 'Miles Davis', 'Kind Of Blue')
Map_set(jazz, 'Duke Ellington', 'Beginning To See The Light')
Map_set(jazz, 'Billy Strayhorn', 'Lush Life')

print "---- List Test ----"
Map_list(jazz)

print "---- Get Test ----"
print Map_get(jazz, 'Miles Davis')
print Map_get(jazz, 'Duke Ellington')
print Map_get(jazz, 'Billy Strayhorn')

print "---- Delete Test ----"
print "** Goodbye Miles"
Map_delete(jazz, "Miles Davis")
Map_list(jazz)

print "** Goodby Duke"
Map_delete(jazz, "Duke Ellington")
Map_list(jazz)

print "** Goodbye Billy"
Map_delete(jazz, "Billy Strayhorn")
Map_list(jazz)

print "** Goodbye Pork Pie Hat"
Map_delete(jazz, "Charles Mingus")

Map_hash()函数的解释例如以下:

This deceptively simple function is the core of how a dict (Map) works. What it does is uses the built-in Python hash function to convert a string to a number. Python uses this function for its own dict data structure, and I'm just reusing it. You should fire up a Python console to see how it works. Once I have a number for the key, I then use the % (modulus) operator and thelen(aMap) to get a bucket where this key can go. As you should know, the % (modulus) operator will divide any number and give me the remainder. I can also use this as a way of limiting giant numbers to a fixed smaller set of other numbers. If you don't get this then use Python to explore it.