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首页Python编程入门:探索Python 3数据处理
Python编程入门:探索Python 3数据处理
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更新于2024-07-16
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“Python for Everybody: Exploring Data in Python 3”是一本面向初学者的数据科学入门书籍,由Charles R. Severance撰写。本书的核心目的是通过Python编程语言教授学生如何处理和探索数据,将编程作为解决电子表格无法解决的复杂数据问题的工具。
书中内容涵盖了Python 3的基础知识,包括变量、数据类型、控制结构(如循环和条件语句)、函数、模块和包的使用。读者将学习如何读取和写入文件,以及如何处理大型数据集,例如通过使用CSV和JSON格式。此外,书中还会讲解网络数据抓取技术,使读者能够从互联网上获取并解析HTML和XML文档,这对于现代数据科学至关重要。
Python作为一种强大的工具,尤其在数据科学领域,它的库如NumPy、Pandas和Matplotlib等,使得数据清洗、分析和可视化变得非常方便。虽然这些高级库不在本书的初级阶段讨论,但理解Python的基础知识是掌握这些库的前提。
书中还涉及了数据库的概念,包括如何使用SQLite,一个轻量级的关系型数据库管理系统,适合于学习和小规模项目。读者将学习SQL查询语言,以查询、更新和管理数据库中的数据,这是数据科学工作流程中不可或缺的一部分。
此外,本书强调实践,鼓励读者通过编写代码和解决实际问题来巩固所学知识。每个章节都包含了一系列练习题,帮助读者应用新学的概念,并提高解决问题的能力。
这本书基于开放许可发布,采用Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License,允许非商业性的分享和改编。作者在附录中详细解释了关于商业和非商业使用的规定,鼓励读者根据自己的需求进行创造性地学习和教学。
“Python for Everybody”是一本非常适合初学者的Python数据科学教材,它提供了一个友好的学习环境,帮助读者逐步建立起编程和数据分析的基本技能,为进一步深入学习数据科学打下坚实基础。
4 CHAPTER 1. WHY SHOULD YOU LEARN TO WRITE PROGRAMS?
As a programmer, your job is to use and orchestrate each of these resources to
solve the problem that you need to solve and analyze the data you get from the
solution. As a programmer you will mostly be “talking” to the CPU and telling
it what to do next. Sometimes you will tell the CPU to use the main memory,
secondary memory, network, or the input/output devices.
Input and
Output
Devices
Software
Main
Memory
Central
Processing
Unit
What
Next?
Network
Secondary
Memory
Figure 1.4: Where Are You?
You need to be the person who answers the CPU’s “What next?” question. But it
would be very uncomfortable to shrink you down to 5mm tall and insert you into
the computer just so you could issue a command three billion times per second. So
instead, you must write down your instructions in advance. We call these stored
instructions a program and the act of writing these instructions down and getting
the instructions to be correct programming.
1.3 Understanding programming
In the rest of this book, we will try to turn you into a p er son who is skilled in the art
of programming. In the end you will be a programmer - perhaps not a professional
programmer, but at least you will have the skills to look at a data/information
analysis problem and develop a program to solve the problem.
In a sense, you need two skills to be a programmer:
• First, you need to know the programming language (Python) - you need to
know the vocabulary and the grammar. You need to be able to spell the
words in this new language properly and know how to construct well-formed
“sentences” in this new language.
• Second, you need to “tell a story”. In writing a story, you combine words
and sentences to convey an idea to the reader. There is a skill and art in
constructing the story, and skill in story writing is improved by doing some
writing and getting some feedback. In programming, our program is the
“story” and the problem you are trying to solve is the “idea”.
Once you learn one programming language such as Python, you will find it much
easier to learn a second programming language such as JavaScript or C++. The
1.4. WORDS AND SENTENCES 5
new programming language has very different vocabulary and grammar but the
problem-solving skills will be the same across all programming languages.
You will learn the “vocabulary” and “sentences” of Python pretty quickly. It will
take longer for you to be able to write a coherent program to solve a brand-new
problem. We teach programming much like we teach writing. We start reading
and explaining programs, then we write simple programs, and then we write in-
creasingly complex programs over time. At some point you “get your muse” and
see the patterns on your own and can see more naturally how to take a problem
and write a program that solves that problem. And once you get to that point,
programming becomes a very pleasant and creative process.
We start with the vocabulary and structure of Python programs. Be patient as
the simple examples remind you of when you started reading for the first time.
1.4 Words and sentences
Unlike human languages, the Python vocabulary is actually pretty small. We call
this “vocabulary” the “reserved words”. These are words that have very special
meaning to Python. When Python sees these words in a Python program, they
have one and only one meaning to Python. Later as you write programs you will
make up your own words that have meaning to you called variables. You will have
great latitude in choosing your names for your variables, but you cannot use any
of Python’s reserved words as a name for a variable.
When we train a dog, we us e special words like “sit”, “stay”, and “fetch”. When
you talk to a dog and don’t use any of the reserved words, they just look at you
with a quizzical look on their face until you say a r eserved word. For example, if
you say, “I wish more people would walk to improve their overall health”, what
most dogs likely hear is, “blah blah blah walk blah blah blah blah.” That is because
“walk” is a reserved word in dog language. Many might suggest that the language
between humans and cats has no reserved words
1
.
The reserved words in the language where humans talk to Python include the
following:
and del global not with
as elif if or yield
assert else import pass
break except in raise
class finally is return
continue for lambda try
def from nonlocal while
That is it, and unlike a dog, Python is already completely trained. When you say
“try”, Python will try every time you say it without fail.
We will learn these reserved words and how they are used in good time, but for
now we will focus on the Python equivalent of “speak” (in human-to-dog language).
The nice thing about telling Python to speak is that we can even tell it what to
say by giving it a message in quotes:
1
http://xkcd.com/231/
6 CHAPTER 1. WHY SHOULD YOU LEARN TO WRITE PROGRAMS?
print(
'Hello world!')
And we have even written our first syntactically correct Python sentence. Our
sentence starts with the function print followed by a string of text of our choosing
enclosed in single quotes. The strings in the print statements are enclosed in quotes.
Single quotes and double quotes do the same thing; most people use single quotes
except in cases like this where a single quote (which is also an apostrophe) appears
in the string.
1.5 Conversing with Python
Now that we have a word and a simple sentence that we know in Python, we need
to know how to start a conversation with Python to test our new language skills.
Before you can converse with Python, you must first install the Python software
on your computer and learn how to start Python on your computer. That is too
much detail for this chapter so I suggest that you consult
www.py4e.com where
I have detailed instructions and screencasts of setting up and starting Python on
Macintosh and Windows systems. At some point, you will be in a terminal or
command window and you will type python and the Python interpreter will start
executing in interactive mode and appear somewhat as follows:
Python
3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25)
[MSC v
.1900 64 bit (AMD64)] on win32
Type
"help", "copyright", "credits" or "license" for more
information.
>>>
The >>> prompt is the Python interpreter’s way of asking you, “What do you want
me to do next?” Python is ready to have a conversation with you. All you have
to know is how to speak the Python language.
Let’s say for example that you did not know even the simplest Python language
words or sentences. You might want to use the standard line that astronauts use
when they land on a faraway planet and try to speak with the inhabitants of the
planet:
>>> I come in peace, please take me to your leader
File "<stdin>", line 1
I come in peace, please take me to your leader
^
SyntaxError: invalid syntax
>>>
This is not going so well. Unless you think of something quickly, the inhabitants
of the planet are likely to stab you with their spears, put you on a spit, roast you
over a fire, and eat you for dinner.
Luckily you brought a copy of this book on your travels, and you thumb to this
very page and try again:
1.5. CONVERSING WITH PYTHON 7
>>> print('Hello world!')
Hello world!
This is looking much better, so you try to communicate some more:
>>> print('You must be the legendary god that comes from the sky')
You must be the legendary god that comes from the sky
>>> print('We have been waiting for you for a long time')
We have been waiting
for you for a long time
>>> print('Our legend says you will be very tasty with mustard')
Our legend says you will be very tasty
with mustard
>>> print 'We will have a feast tonight unless you say
File "<stdin>", line 1
print '
We will have a feast tonight unless you say
^
SyntaxError: Missing parentheses in call to 'print'
>>>
The conversation was going so well for a while and then you made the tiniest
mistake using the Python language and Python brought the spears back out.
At this point, you should also realize that while Python is amazingly complex and
powerful and very picky about the syntax you use to communicate with it, Python
is not intelligent. You are really just having a conversation with yourself, but using
proper syntax.
In a sense, when you use a program written by someone else the conversation is
between you and those other programmers with Python acting as an intermediary.
Python is a way for the creators of programs to express how the conversation is
supposed to proceed. And in just a few more chapters, you will be one of those
programmers using Python to talk to the users of your program.
Before we leave our first conversation with the Python interpreter, you should prob-
ably know the proper way to say “good-bye” when interacting with the inhabitants
of Planet Python:
>>> good-bye
Traceback (most recent call last):
File
"<stdin>", line 1, in <module>
NameError: name 'good' is not defined
>>> if you don't mind, I need to leave
File "<stdin>", line 1
if you don'
t mind, I need to leave
^
SyntaxError: invalid syntax
>>> quit()
You will notice that the error is different for the first two incorrect attempts. The
second error is different because if is a reserved word and Python saw the reserved
word and thought we were trying to say something but got the syntax of the
sentence wrong.
8 CHAPTER 1. WHY SHOULD YOU LEARN TO WRITE PROGRAMS?
The proper way to say “good-bye” to Python is to enter quit() at the interactive
chevron >>> prompt. It would have probably taken you quite a while to guess that
one, so having a book handy probably will turn out to be helpful.
1.6 Terminology: Interpreter and compiler
Python is a high-level language intended to be relatively straightforward for hu-
mans to read and write and for computers to read and process. Other high-level
languages include Java, C++, PHP, Ruby, Basic, Perl, JavaScript, and many more.
The actual hardware inside the Central Processing Unit (CPU) does not under-
stand any of these high-level languages.
The CPU understands a language we call machine language. Machine language is
very simple and frankly very tiresome to write because it is represented all in zeros
and ones:
001010001110100100101010000001111
11100110000011101010010101101101
...
Machine language seems quite simple on the surface, given that there are only zeros
and ones, but its syntax is even more complex and far more intricate than Python.
So very few programmers ever write machine language. Instead we build various
translators to allow programmers to write in high-level languages like Python or
JavaScript and these translators convert the programs to machine language for
actual execution by the CPU.
Since machine language is tied to the computer hardware, machine language is not
portable across different types of hardware. Programs written in high-level lan-
guages can be moved between different computers by using a different interpreter
on the new machine or recompiling the code to create a machine language version
of the program for the new machine.
These programming language translators fall into two general categories: (1) inter-
preters and (2) compilers.
An interpreter reads the source code of the program as written by the programmer,
parses the source code, and interprets the instructions on the fly. Python is an
interpreter and when we are running Python interactively, we can type a line of
Python (a sentence) and Python processes it immediately and is ready for us to
type another line of Python.
Some of the lines of Python tell Python that you want it to remember some value
for later. We need to pick a name for that value to be remembered and we can use
that symbolic name to retrieve the value later. We use the term variable to refer
to the labels we use to refer to this stored data.
>>> x = 6
>>> print(x)
6
>>> y = x * 7
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