Python实战（八）

一实战——列表操作

1 ex38.py

ten_things = "Apples Oranges Crows Telephone Light Sugar"
print "Wait there are not 10 things in that list. Let's fix that."
stuff = ten_things.split(' ')
more_stuff = ["Day", "Night", "Song", "Frisbee", "Corn", "Banana", "Girl", "Boy"]
while len(stuff) != 10:
    next_one = more_stuff.pop()
    print "Adding: ", next_one
    stuff.append(next_one)
    print "There are %d items now." % len(stuff)
print "There we go: ", stuff
print "Let's do some things with stuff."
print stuff[1]
print stuff[-1] # whoa! fancy
print stuff.pop()
print ' '.join(stuff) # what? cool!
print '#'.join(stuff[3:5]) # super stellar!

2 运行结果

PS E:\Python\exercise> python ex38.py
Wait there are not 10 things in that list. Let's fix that.
Adding:  Boy
There are 7 items now.
Adding:  Girl
There are 8 items now.
Adding:  Banana
There are 9 items now.
Adding:  Corn
There are 10 items now.
There we go:  ['Apples', 'Oranges', 'Crows', 'Telephone', 'Light', 'Sugar', 'Boy', 'Girl', 'Banana', 'Corn']
Let's do some things with stuff.
Oranges
Corn
Corn
Apples Oranges Crows Telephone Light Sugar Boy Girl Banana
Telephone#Light

二实战——字典,可爱的字典

1 一些关于字典的例子

PS E:\Python\exercise> python
Python 2.7.15 (v2.7.15:ca079a3ea3, Apr 30 2018, 16:30:26) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> stuff = {'name': 'Zed', 'age': 39, 'height': 6 * 12 + 2}
>>> print stuff['name']
Zed
>>> print stuff['age']
39
>>> print stuff['height']
74
>>> stuff['city'] = "San Francisco"
>>> print stuff['city']
San Francisco
>>> stuff[1] = "Wow"
>>> stuff[2] = "Neato"
>>> print stuff[1]
Wow
>>> print stuff[2]
Neato
>>> stuff
{'city': 'San Francisco', 2: 'Neato', 'name': 'Zed', 1: 'Wow', 'age': 39, 'height': 74}
>>> del stuff['city']
>>> del stuff[1]
>>> del stuff[2]
>>> stuff
{'name': 'Zed', 'age': 39, 'height': 74}

2 ex39.py

# create a mapping of state to abbreviation
states = {
    'Oregon': 'OR',
    'Florida': 'FL',
    'California': 'CA',
    'New York': 'NY',
    'Michigan': 'MI'
}
# create a basic set of states and some cities in them
cities = {
    'CA': 'San Francisco',
    'MI': 'Detroit',
    'FL': 'Jacksonville'
}
# add some more cities
cities['NY'] = 'New York'
cities['OR'] = 'Portland'
# print out some cities
print '-' * 10
print "NY State has: ", cities['NY']
print "OR State has: ", cities['OR']
# print some states
print '-' * 10
print "Michigan's abbreviation is: ", states['Michigan']
print "Florida's abbreviation is: ", states['Florida']
# do it by using the state then cities dict
print '-' * 10
print "Michigan has: ", cities[states['Michigan']]
print "Florida has: ", cities[states['Florida']]
# print every state abbreviation
print '-' * 10
for state, abbrev in states.items():
    print "%s is abbreviated %s" % (state, abbrev)
# print every city in state
print '-' * 10
for abbrev, city in cities.items():
    print "%s has the city %s" % (abbrev, city)
# now do both at the same time
print '-' * 10
for state, abbrev in states.items():
    print "%s state is abbreviated %s and has city %s" % (
        state, abbrev, cities[abbrev])
print '-' * 10
# safely get a abbreviation by state that might not be there
state = states.get('Texas')
if not state:
    print "Sorry, no Texas."
# get a city with a default value
city = cities.get('TX', 'Does Not Exist')
print "The city for the state 'TX' is: %s" % city

3 运行结果

PS E:\Python\exercise> python ex39.py
----------
NY State has:  New York
OR State has:  Portland
----------
Michigan's abbreviation is:  MI
Florida's abbreviation is:  FL
----------
Michigan has:  Detroit
Florida has:  Jacksonville
----------
California is abbreviated CA
Michigan is abbreviated MI
New York is abbreviated NY
Florida is abbreviated FL
Oregon is abbreviated OR
----------
FL has the city Jacksonville
CA has the city San Francisco
MI has the city Detroit
OR has the city Portland
NY has the city New York
----------
California state is abbreviated CA and has city San Francisco
Michigan state is abbreviated MI and has city Detroit
New York state is abbreviated NY and has city New York
Florida state is abbreviated FL and has city Jacksonville
Oregon state is abbreviated OR and has city Portland
----------
Sorry, no Texas.
The city for the state 'TX' is: Does Not Exist

4 hashmap.py

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

def get_bucket(aMap, key):
    """Given a key, find the bucket where it would go."""
    bucket_id = hash_key(aMap, key)
    return aMap[bucket_id]
    
def get_slot(aMap, key, default=None):
    """
    Returns the index, key, and value of a slot found in a bucket.
    Returns -1, key, and default (None if not set) when not found.
    """
    bucket = get_bucket(aMap, key)
    for i, kv in enumerate(bucket):
        k, v = kv
        if key == k:
            return i, k, v
    return -1, key, default

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

def set(aMap, key, value):
    """Sets the key to the value, replacing any existing value."""
    bucket = get_bucket(aMap, key)
    i, k, v = get_slot(aMap, key)
    if i >= 0:
        # the key exists, replace it
        bucket[i] = (key, value)
    else:
        # the key does not, append to create it
        bucket.append((key, value))

def delete(aMap, key):
    """Deletes the given key from the Map."""
    bucket = get_bucket(aMap, key)
    for i in xrange(len(bucket)):
        k, v = bucket[i]
        if key == k:
            del bucket[i]
            break
    
def list(aMap):
    """Prints out what's in the Map."""
    for bucket in aMap:
        if bucket:
            for k, v in bucket:
                print k, v

5 ex39_test.py

import hashmap
# create a mapping of state to abbreviation
states = hashmap.new()
hashmap.set(states, 'Oregon', 'OR')
hashmap.set(states, 'Florida', 'FL')
hashmap.set(states, 'California', 'CA')
hashmap.set(states, 'New York', 'NY')
hashmap.set(states, 'Michigan', 'MI')

# create a basic set of states and some cities in them
cities = hashmap.new()
hashmap.set(cities, 'CA', 'San Francisco')
hashmap.set(cities, 'MI', 'Detroit')
hashmap.set(cities, 'FL', 'Jacksonville')

# add some more cities
hashmap.set(cities, 'NY', 'New York')
hashmap.set(cities, 'OR', 'Portland')

# print out some cities
print '-' * 10
print "NY State has: %s" % hashmap.get(cities, 'NY')
print "OR State has: %s" % hashmap.get(cities, 'OR')

# print some states
print '-' * 10
print "Michigan's abbreviation is: %s" % hashmap.get(states, 'Michigan')
print "Florida's abbreviation is: %s" % hashmap.get(states, 'Florida')

# do it by using the state then cities dict
print '-' * 10
print "Michigan has: %s" % hashmap.get(cities, hashmap.get(states, 'Michigan'))
print "Florida has: %s" % hashmap.get(cities, hashmap.get(states, 'Florida'))

# print every state abbreviation
print '-' * 10
hashmap.list(states)

# print every city in state
print '-' * 10
hashmap.list(cities)
print '-' * 10
state = hashmap.get(states, 'Texas')
if not state:
    print "Sorry, no Texas."
# default values using ||= with the nil result
# can you do this on one line?
city = hashmap.get(cities, 'TX', 'Does Not Exist')
print "The city for the state 'TX' is: %s" % city

6 运行结果

PS E:\Python\exercise> python ex39_test.py
----------
NY State has: New York
OR State has: Portland
----------
Michigan's abbreviation is: MI
Florida's abbreviation is: FL
----------
Michigan has: Detroit
Florida has: Jacksonville
----------
California CA
New York NY
Michigan MI
Oregon OR
Florida FL
----------
FL Jacksonville
NY New York
CA San Francisco
OR Portland
MI Detroit
----------
Sorry, no Texas.
The city for the state 'TX' is: Does Not Exist

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