Python Basics

Presented by Jun Ding

Aug, 2015

Why Python？

Easy 2 LearnCoding FastSimple Syntax…..

Install it? Simple!(1) For Linux Users (e.g. Ubuntu）

The python is installed by default for most Linux OS.

If not, you can easily install it by using the following command:

sudo apt-get install python (Debian/Ubuntu)

sudo yum install python (ReaHat/CentOS/Fedora)

(2) Windows and Mac OS Users

Just download the python from it’s website

http://www.python.org/download/releases/2.7.6/

Double click to install it. That’s it.

Is there any books/tutorials very helpful?

(1) OnLine tutorial

http://www.learnpython.org/

(2) Book

Dive into Python

Where to start?Let’s try a few simple examples to show how simple

python is.

(1) Print “Hello World!”

(2) Calculate 10+26,26.2/15

Basic Syntax-DataType

Too boring to learn the grammar?

No! you don’t have to do that. Let’s just see a few

examples. You will find there is no “learning” grammar

at all.

Data type:

int e.g. 7

float e.g. 7.1

string “I am a string”

Basic container:

list (*) A=[1,2,3,4]

Tuple (a special case of list, immutable list)

dictionary D={‘A’:0,’C’:1,’G’:2,’T’:3}

(Example1.py)

From the above example, we have seen :

（1） int : lengthA=6

(2) float: Element in A is float A[0]=4.0

(3) Boolean: AGB –True of False

(4) List

Basic Syntax-ListList is almost the most important DataType in Python.

Almost, for all kinds of data, you can store them in List.

A=[4.0,6.0,7.0,9.7,1.2]

There are many important List functions, which you

need to know. We will study them in the following

example. (UseList.py)

Basic Syntax-List

*Things to remember*:

• A[x], get element in list A at position x

• A.append(x), append x to A list

• A.insert(p,x), insert x to A at position p

• A. index(x), get the first position of x in A, error it not found

• A.count(x), get the occurrence of x in A

• A.sort(reverse=True/False), sort list A. True/False set the

sorting order.

• A[x:y] , get the subset of list A from position x to position y.

Basic Syntax-StringThere are lots of operations to string. We will discuss

about some important string operations.

We will also learn them from an example

Basic Syntax-String

Basic Syntax-String

*Things to remember*:

• A[x], get the element at position x of A

• len(A), get the length of string A

• A.upper(), get all uppercase of string A

• A.lower(), get all lowercase of string A

• A.split(), split string A with specific separator.

• .join(Asplit), join the list of strings with the separator

-> string

• A[x:y] the substring of A from x to y

Basic Syntax-flow control

There are 3 important types of flow-control

(1) If

(2) for

(3) While

Please see example code(controlFlow.py)

Basic Syntax-flow control

Basic Syntax-flow control

*Things need to remember*:

(1) if-else

if (condition A):

statement A

else:

statement B

(1) For

for i in A:

statement A

(1) While

while(condition A):

statement B

Basic Syntax- List comprehension

This is a useful technique regarding to python list

A=[1,2,3,4,5]

If we want to get the sublets of A, in which all

elements >3. How did we do this

See example code listcomprehension.py

Basic Syntax- List comprehension

Basic Syntax-mathBasic math in python

+,-,*,/,**,sqrt(),and etc.

See the following example code of math

(math.py)

Basic Syntax-math

Basic Syntax-Function

Python function is very important, it can help you to

organize your code well and improve the efficiency.

Please see the code example

(UseFunction.py)

Basic Syntax-Function

Basic Syntax-Function

*Things to remember*:

Please try to use function as possible as you can.

It can improve the re-usability of your code.

You don’t need to code the same function twice if it

already implemented.

Basic Syntax-Files

Handling files is also important.

Unlike in java/c++, handling files in python is easy.

(1) read in files

(2) write files

Please see the example code in HandleFile.py

Basic Syntax-Files

Basic Syntax-Files

*Things to remember*:

(1) Input

f=open(“filename”,’r’)

lf=f.readlines()

f.close()

(2) Output

f=open(“filename”,’w’)

f.write(String)

f.close()

Congrats!, you are done with

Python Basics

Do your homework:

(1) Try toy example codes from

http://www.learnpython.org/

(2) Get familiar with the functions mentioned in this

slides

(3) In the next class, we will study on solving real

problems by using python. ( You might be asked to

write some simple code, so please be prepared).

Questions ?