Python Tutorial for Beginners

Python Tutorial

Unlike Matlab, Python is not dependent any development environment.

First enter into the shell chosen from the introduction.
Now We'll make a small examples:

The print function, (\n allows linebreak):
In [1]: print "a\nb\nc\n"
Out [1]:
 a
 b
 c

 You can also write several rows code in IPython, and activate whole
At once by pressing ctrl-enter at the end of every line, and than press enter for activate
The code section:

In [2]: print "Discover"
print "SDK"

Out [2]:
Discover
SDK

What we do When IPython stuck?

L-Ctrl -> erases the commande window, and fix the stuck.

.-Ctrl - initializes the IPython without closing the user interface.

Numbers:

Basically you can perform arithmetic operations on the command line:

#In [2]: 5 * (10 + 1)
 Out[2]: 55

Notice that unlike other programming languages, there is no need to set numbers by type. On the one hand it’s more user-friendly and allows easy operation. and on the other hand it’s necessary to define variables with significant names that Include the numbers type.

For example:

Modulo with float type:

In [3]: 7.24 % 3 
Out[3]: 1.2400000000000002

power of two numbers:

In [4]: 5**2
Out[4]: 25

Automatic conversion:

>>> a=3 {int}
>>> b=5.3 {float}
>>> c=a+b 
>>> c =>8.3   {c type is float}

>>> a=2.0
>>> b=3.0
>>> (a+b)/2
2.5

 Application of Variables:

In [5]: a = 2 
In [6]: a /= 2 
In [7]: a 
Out[7]: 1 

The following function receives a variable and returns its type:

>>> type(13.4)
<type 'float'>
>>> type('hello')
<type 'str'>

Lists:

In [1]: lst = [1, 2, 3,5,6,7]
In [2]: type(lst)
Out[2]: list 

Create List Can be done by the function range():

In [3]: range(7)
Out[3]: [0, 1, 2, 3, 4, 5, 6]

In [4]: lst = range(10, 30, 3) 
In [5]: lst 
Out[5]: [10, 13, 16, 19, 22, 25, 28] 

Keeping in mind that starting from zero, the range does not include the target index:

In [6]: lst[3:9] 
Out[6]: [19, 22, 25, 28] 

Connecting between the two lists is defined as a combination of list:

In [7]: a=[21, 22, 23, 24, 25] 
In [8]: b=[26, 27, 28, 29,29] 
In [9]: a + b 
Out[9]: [21, 22, 23, 24, 25,26, 27, 28, 29,29] 

Tuples:

At first sight behave like a list, only with round brackets instead

Square. 

In [1]: b = (7, 6,5, 4) 
In [2]: b 
Out[3]: (7, 6, 5, 4

 The main difference is they are immutable:

b[1]=2
TypeError: 'tuple' object does not support item assignment

Call by refernce:

The most programming languages adopt this method.

No need to write a special way to achieve Speed and efficiency.

You have to remember only one thing - Mounting variables) as well as transfer

Arguments to functions (no copy, if you want a copy, must be made It explicitly.

In Matlab situation is reversed. Always being copied, if you want to improve

Speed or save memory, need to learn techniques,(for example, Local  functions).

In [1]: a = [a, 2, 'cmd'] 
In [2]: b = a 
In [3]: b[1] = 400 ------------------------>  a changed
In [4]: a 
Out[4]: [10, 400, 'cmd'] 

Strings:

Can be viewed in two equivalent main forms

In [1]: "Discover SDK" 
In[2]: 'Discover SDK' 

Connect strings with each other but not with a number

In [3]: g = 'Dsicover'
In [4]: f = 'SDK' 
In [5]: g + f 
Out[5]: 'DiscoverSDK' 
In [6]: g + ' ' + f 
Out[6]: 'Discover SDK' 

In [6] a="sdk"
Out[6] a+5
TypeError: cannot concatenate 'str' and 'int' objects

Multiplication:

In [42]: 'sDk' * 3 
Out[42]: 'sDksDksDk'

Conditions:

One special features of the Python language is Running condition code by indentation.

if b > a:
  print '"a" is small and equal to %s' %a
else:
  print '"b" is small and equal to %s' %b

For several conditions(Note that displacement Is crucial) :

>>> x=100
>>> y=200
>>> c=300
>>> if  x<y  and  y<c:
	print "the maximum number is c"
elif  y<x  and  c<x:
	print "the maximum number is x"
elif  x<y  and  c<y:
	print "the maximum number is y"

 the maximum number is c

loops:

For:

Different from other languages, for-loops do not promote the loop index. But going through the parts list: 

In [1]: a=['a','b','c','d','e']
In [2]: for i in a:
	      print(i)
Out[2]:	
a
b
c
d
e

In [1]: for i in range(5):
	    print "%d\n" %i

Out[1]:	
0

1

2

3

4

While:

While loop ran continuously until the Loop condition return True value.

>>> A=7
>>> while A < 10:
	A+=1
	
>>> A
10

Another common use is to create an infinite loop:

>>> a=4
>>> b=5
>>> while True:
	if a==b:
		break
	a+=1
	
>>> a
5

break,continue :

continue, promoting  to the next iteration.
Break command, goes out of the loop.

>>> a=4
>>> b=5
>>> while a<b:
	a+=1
	if (b==a):
		break

>>> a
5

>>> for st in ['Discover','SDK','Cloud']:
	if st!='SDK':
		continue
	else:
		break
	
>>> st
'SDK'

Functions:

Now we use more IDE - Write code to the file by editor. You can
Write in IDLE, PyScripter, spyder or pycharm and run through.
You can also run through a DOS window of Windows, or through the IPython.

As usual indentation is necessary:

>>> def Num_plus_1(num):
	num+=1
	print "%d" %num

>>> Num_plus_1(4)
5

>>>def max1(a,b):
	if a>b:
		return a
	return b

>>> max1(1,9)
9

 Global and local Variables

Variables defined in a function are local variables.

To define a global variable we use the following command.

Definition of a global variable:

global Var

If we'll try to change a global variable in a function, the verianble will not change and  a local variable with the same value will created:

>>> def Local(a):
	b=34
	a=b------> Local variable
	return a

>>> local(a)
34
>>> a-------> The vlaue of the global variable has'nt changed
54

It is possible to change a global variable in the function:

>>> global a
>>> a=54
>>> def glob():
	global a
	a=34
	return

>>> a
54
>>> glob()
>>> a
34
>>> 

 In case "a" does not exist. It will created inside the function.

• Note that the use of global variables in such a manner is not recommended

 Logical Expressions

simple use of logical expressions

>>> 2!=4
True
>>> 3>2
True
>>> 2>3
False
>>> 2!=2
False

 the Not operator: 

>>> not 10<5
True
>>> not 5!=5
True

Easy and Effective way to find out if an organ is on the list:

>>> list1=[0,1,2,3,4,5,6,7,8,9]
>>> 10 in list1
False
>>> 2 in list1
True

A similar implementation for strings:

>>> str= "Discover SDK"
>>> 'SDK' in str
True
>>> 'discover' in str
False

Python defines a relationship between strings, and a relationship based on
Organ between lists and tuples:

>>> 'e'>'d'>'a'
True
>>> 'H'>'G'>='A'=='A'
True
>>> [1,5,8]>[1,5,6]
True
>>> [50] > [1,2,3,4,5,6,7]
True