书名：Python自然语言处理（影印版）

作者：Steven Bird, Ewan Klein, Edward Loper 著

国内出版社：东南大学出版社

出版时间：2010年09月

页数：479

书号：978-7-5641-2261-4

原版书出版商：O'Reilly Media

 

Steven Bird是墨尔本大学计算机科学和软件工程系副教授，宾夕法尼亚大学语言学数据联盟高级研究助理。

 

 

 

Ewan Klein是爱丁堡大学信息学院语言技术教授。

 

 

 

Edward Loper是毕业于宾夕法尼亚大学专注于机器学习的自然语言处理方向的博士，现在在波士顿的BBN Technologies担任研究员。

 

 

The animal on the cover of Natural Language Processing with Python is a right whale,
the rarest of all large whales. It is identifiable by its enormous head, which can measure
up to one-third of its total body length. It lives in temperate and cool seas in both
hemispheres at the surface of the ocean. It’s believed that the right whale may have
gotten its name from whalers who thought that it was the “right” whale to kill for oil.
Even though it has been protected since the 1930s, the right whale is still the most
endangered of all the great whales.
The large and bulky right whale is easily distinguished from other whales by the calluses
on its head. It has a broad back without a dorsal fin and a long arching mouth that begins above the eye. Its body is black, except for a white patch on its belly. Wounds
and scars may appear bright orange, often becoming infested with whale lice or
cyamids. The calluses—which are also found near the blowholes, above the eyes, and
on the chin, and upper lip—are black or gray. It has large flippers that are shaped like
paddles, and a distinctive V-shaped blow, caused by the widely spaced blowholes on
the top of its head, which rises to 16 feet above the ocean’s surface.
The right whale feeds on planktonic organisms, including shrimp-like krill and copepods.
As baleen whales, they have a series of 225–250 fringed overlapping plates hanging
from each side of the upper jaw, where teeth would otherwise be located. The plates
are black and can be as long as 7.2 feet. Right whales are “grazers of the sea,” often
swimming slowly with their mouths open. As water flows into the mouth and through
the baleen, prey is trapped near the tongue.
Because females are not sexually mature until 10 years of age and they give birth to a
single calf after a year-long pregnancy, populations grow slowly. The young right whale
stays with its mother for one year.
Right whales are found worldwide but in very small numbers. A right whale is commonly
found alone or in small groups of 1 to 3, but when courting, they may form
groups of up to 30. Like most baleen whales, they are seasonally migratory. They inhabit
colder waters for feeding and then migrate to warmer waters for breeding and calving.
Although they may move far out to sea during feeding seasons, right whales give birth
in coastal areas. Interestingly, many of the females do not return to these coastal breeding
areas every year, but visit the area only in calving years. Where they go in other
years remains a mystery.
The right whale’s only predators are orcas and humans. When danger lurks, a group
of right whales may come together in a circle, with their tails pointing outward, to deter
a predator. This defense is not always successful and calves are occasionally separated
from their mother and killed.
Right whales are among the slowest swimming whales, although they may reach speeds
up to 10 mph in short spurts. They can dive to at least 1,000 feet and can stay submerged
for up to 40 minutes. The right whale is extremely endangered, even after years of
protected status. Only in the past 15 years is there evidence of a population recovery
in the Southern Hemisphere, and it is still not known if the right whale will survive at
all in the Northern Hemisphere. Although not presently hunted, current conservation
problems include collisions with ships, conflicts with fishing activities, habitat destruction,
oil drilling, and possible competition from other whale species. Right whales
have no teeth, so ear bones and, in some cases, eye lenses can be used to estimate the
age of a right whale at death. It is believed that right whales live at least 50 years, but
there is little data on their longevity.