Python for Informatics：数据探索与分析入门

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"Python for Informatics" 是一本关于Python编程的入门书籍，专注于数据探索与分析。本书由Charles Severance编写，自2009年以来经过多次修订，旨在让读者尽快接触并解决数据分析问题。书中包含一系列关于数据分析的运行示例和练习，从一开始就引入了这一主题。在书中，作者首先介绍了Python的基础知识，如变量、控制结构（如循环和条件语句）、函数等，帮助初学者建立编程思维。随着内容的深入，书中的章节涵盖了数据结构（如列表、元组、字典和集合）、文件操作、异常处理以及模块和包的使用，这些都是进行数据分析前必备的基础知识。特别地，2013年的修订版中，第13章和第14章重点转向了JSON（JavaScript Object Notation）的使用，这是一种轻量级的数据交换格式，常用于数据的存储和传输。同时，书中也涉及了OAuth，一种授权框架，对于获取和处理网络数据非常关键。新增的章节关注数据可视化，这是数据分析中重要的环节，通过图形化数据来揭示隐藏的模式和趋势。在学习过程中，读者将逐步掌握如何利用Python进行数据的读取、清洗、处理、分析以及可视化。这些技能不仅适用于科学研究，还对商业决策、市场分析等领域有着广泛的应用。此外，书中的例子和练习旨在鼓励读者实践，从而更好地理解和应用所学知识。这本书遵循了Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License，允许非商业性的复制、分发和修改，但需保留原作者的署名，并同样遵循相同的许可协议。这使得教育资源得以广泛共享，促进学习社区的发展。通过阅读和实践"Python for Informatics"，读者不仅能掌握Python编程基础，还能具备处理和分析信息的能力，为在信息时代解决问题提供有力工具。无论是对计算机科学感兴趣的初学者，还是希望提升数据分析技能的专业人士，这本书都是一个很好的起点。

2 Chapter 1. Why should you learn to write programs?

For example, look at the ﬁrst three paragraphs of this chapter and tell me the most

commonly used word and how many times the word is used. While you were

able to read and understand the words in a few seconds, counting them is almost

painful because it is not the kind of problem that human minds are designed to

solve. For a computer the opposite is true, reading and understanding text from a

piece of paper is hard for a computer to do but counting the words and telling you

how many times the most used word was used is very easy for the computer:

python words.py

Enter file:words.txt

to 16

Our “personal information analysis assistant” quickly told us that the word “to”

was used sixteen times in the ﬁrst three paragraphs of this chapter.

This very fact that computers are good at things that humans are not is why you

need to become skilled at talking “computer language”. Once you learn this new

language, you can delegate mundane tasks to your partner (the computer), leaving

more time for you to do the things that you are uniquely suited for. You bring

creativity, intuition, and inventiveness to this partnership.

1.1 Creativity and motivation

While this book is not intended for professional programmers, professional pro-

gramming can be a very rewarding job both ﬁnancially and personally. Building

useful, elegant, and clever programs for others to use is a very creative activity.

Your computer or Personal Digital Assistant (PDA) usually contains many differ-

ent programs from many different groups of programmers, each competing f or

your attention and interest. They try their best to meet your needs and give you a

great user experience in the process. In some situations, when you choose a piece

of software, the programmers are directly compensated because of your choice.

If we think of programs as the creative output of groups of pr ogrammers, perhaps

the following ﬁgure is a more sensible version of our PDA:

Me!

PDA

Me!

Pick Pick Pick

BuyPickPick

Me!

Me :)

Me!

For now, our primary motivation is not to make money or please end-users, but in-

stead for us to be more productive in handling the data and information that we will

encounter in our lives. When you ﬁrst start, you will be both the programmer and

end-user of your programs. As you gain skill as a programmer and programming

feels more creative to you, your thoughts may turn toward developing programs

for others.

1.4. Words and sentences 5

• 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 pr ogramming language such as JavaScript or C++. T he

new programming language has very different vocabulary and grammar but once

you learn problem solving skills, they 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 and then we write simple programs and then 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 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.

In a sense, when we train a dog, we would use special words like, “sit”, “stay”,

and “fetch”. Also 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 faces until you say a reserved

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

The reserved words in the language where humans talk to Python incudes the

following:

http://xkcd.com/231/

6 Chapter 1. Why should you learn to write programs?

and del for is raise

assert elif from lambda return

break else global not try

class except if or while

continue exec import pass yield

def nally in print

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 lan-

guage). 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:

Hello world!

And we have even written our ﬁrst syntactically correct Python sentence. Our

sentence starts with the reserved word print followed by a string of text of our

choosing enclosed in single quotes.

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.pythonlearn.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 2.6.1 (r261:67515, Jun 24 2010, 21:47:49)

[GCC 4.2.1 (Apple Inc. build 5646)] on darwin

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 and you can have a conversation.

Lets 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 far away planet and try to speak with the inhabitants of the

planet:

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