第4章 当索引行不通时

代码清单4-1 字典示例

# A simple database

# A dictionary with person names as keys. Each person is represented as
# another dictionary with the keys 'phone' and 'addr' referring to their phone
# number and address, respectively.
people = {

    'Alice': {
        'phone': '2341',
        'addr': 'Foo drive 23'
    },

    'Beth': {
        'phone': '9102',
        'addr': 'Bar street 42'
    },

    'Cecil': {
        'phone': '3158',
        'addr': 'Baz avenue 90'
    }

}

# Descriptive labels for the phone number and address. These will be used
# when printing the output.
labels = {
    'phone': 'phone number',
    'addr': 'address'
}

name = input('Name: ')

# Are we looking for a phone number or an address?
request = input('Phone number (p) or address (a)? ')

# Use the correct key:
if request == 'p': key = 'phone'
if request == 'a': key = 'addr'

# Only try to print information if the name is a valid key in
# our dictionary:
if name in people: print("{}'s {} is {}.".format(name, labels[key], people[name][key]))

运行结果如下：

Name: Beth
Phone number (p) or address (a)? p
Beth's phone number is 9102.

代码清单4-2 字典方法示例

# A simple database using get()

# Insert database (people) from Listing 4-1 here.
people = {

    'Alice': {
        'phone': '2341',
        'addr': 'Foo drive 23'
    },

    'Beth': {
        'phone': '9102',
        'addr': 'Bar street 42'
    },

    'Cecil': {
        'phone': '3158',
        'addr': 'Baz avenue 90'
    }

}

labels = {
    'phone': 'phone number',
    'addr': 'address'
}

name = input('Name: ')

# Are we looking for a phone number or an address?
request = input('Phone number (p) or address (a)? ')

# Use the correct key:
key = request # In case the request is neither 'p' nor 'a'
if request == 'p': key = 'phone'
if request == 'a': key = 'addr'

# Use get to provide default values:
person = people.get(name, {})
label = labels.get(key, key)
result = person.get(key, 'not available')

print("{}'s {} is {}.".format(name, label, result))

运行结果如下：

Name: Gumby
Phone number (p) or address (a)? batting average
Gumby's batting average is not available.