2022/1/5 fluent python开始

colors = ['black', 'white']
sizes = ['s', 'm', 'l']
tshirts = [(color, size) for color in colors for size in sizes]
print(tshirts)
#列表推导的作用只有一个，生成列表。

#生成器表达式初始化元组和数据
symbols = '@#$%&'
s = tuple(ord(symbol) for symbol in symbols)
print(s)
import array
q = array.array('i', (ord(symbol) for symbol in symbols))
print(q)

#使用生成器表达式计算笛卡尔坐标
colors = ['black', 'white']
sizes = ['s', 'm', 'l']
for tshirt in ('%s %s'%(c, s) for c in colors for s in sizes):
    print(tshirt)

#把元组用作记录 元组拆包
lax_coordinates = (33.9425, -118.408056)
city, year ,pop,chg,area = ('tokyo',2003,32450,0.66,8014)
traveler_ids = [('usa','31195855'),('bra','ce342567'),('sep', 'xda205856')]
for passport in sorted(traveler_ids):
    print('%s/%s' % passport )
for country, _ in traveler_ids:
    print(country)

#元组拆包
lax_coordinates = (33.9425, -118.408056)
latitude, longitude = lax_coordinates
print(latitude, longitude)

import os
_, filename = os.path.split('/home/luciano/.ssh/idrsa.pub')
print(filename)
# _ *args 占位符
a, b, *rest = range(5)
print(a, b, rest)
a, b, *rest = range(3)
print(a, b, rest)
a, b, *rest = range(2)
print(a, b, rest)

a,*body, c, d = range(5)
print(a,body, c, d)
#嵌套元组拆包
#用嵌套元组获得经纬度
metro_areas =[
    ('tokyo', 'jp', 36.933,(35.689722,139691667)),
    ('delhi ncr', 'in', 21.935,(28.613889,77208889)),
    ('mexico city','mx',20.142,(19.433333,-99.133333)),
    ('new york','us',20.104,(40.808611,-74.020386)),
    ('sao paulo','br',19.649,(-23.547778,-46.635833)),
]
print('{:15} | {:^9} | {:^9}'.format('', 'lat.', 'long.'))#0表示序号，格式化字符，15代表宽度，^代表ju中
fmt = '{:15} | {:9.4f} | {:9.4f}' #.4表示小数为四位，
for name, cc, pop, (latitude, longitude) in metro_areas:
    if longitude <= 0:
        print(fmt.format(name, latitude, longitude))