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DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, Language Fundamentals Introduction Python is a general purpose high level programming language. Python was developed by Guido Van Rossam in 1989 while working at National Research Institute at Netherlands. But officially Python was made available to public in 1991. The official Date of Birth for Python is : Feb 20th 1991. Python is recommended as first programming language for beginners. Eg1: To print Helloworld: Java: 1 ) public class HelloWorld 2 ) { 3 ) p s v main(String[] args) 4 ) { 5 ) SOP("Hello world"); 6 ) } 7 ) } C: 1 ) #include<stdio.h> 2 ) void main() 3 ) { 4 ) print("Hello world"); 5 ) } Python: print("Hello World")
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, Eg2: To print the sum of 2 numbers Java: 1 ) public class Add 2 ) { 3 ) public static void main(String[] args) 4 ) { 5 ) int a,b; 6 ) a = 10 ; 7 ) b= 20 ; 8 ) System.out.println("The Sum:"+(a+b)); 9 ) } 10 ) } C: 1 ) #include <stdio.h> 2 ) 3 ) void main() 4 ) { 5 ) int a,b; 6 ) a =10; 7 ) b=20; 8 ) printf("The Sum:%d",(a+b)); 9 ) } Python: 1 ) a= 10 2 ) b= 20 3 ) print("The Sum:",(a+b)) The name Python was selected from the TV Show "The Complete Monty Python's Circus", which was broadcasted in BBC from 1969 to 1974. Guido developed Python language by taking almost all programming features from different languages
- Functional Programming Features from C
- Object Oriented Programming Features from C++
- Scripting Language Features from Perl and Shell Script
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
3. High Level Programming language:
Python is high level programming language and hence it is programmer friendly language. Being a programmer we are not required to concentrate low level activities like memory management and security etc..
4. Platform Independent:
Once we write a Python program,it can run on any platform without rewriting once again. Internally PVM is responsible to convert into machine understandable form.
5. Portability:
Python programs are portable. ie we can migrate from one platform to another platform very easily. Python programs will provide same results on any paltform.
6. Dynamically Typed:
In Python we are not required to declare type for variables. Whenever we are assigning the value, based on value, type will be allocated automatically.Hence Python is considered as dynamically typed language. But Java, C etc are Statically Typed Languages b'z we have to provide type at the beginning only. This dynamic typing nature will provide more flexibility to the programmer.
7. Both Procedure Oriented and Object Oriented:
Python language supports both Procedure oriented (like C, pascal etc) and object oriented (like C++,Java) features. Hence we can get benefits of both like security and reusability etc
8. Interpreted:
We are not required to compile Python programs explcitly. Internally Python interpreter will take care that compilation. If compilation fails interpreter raised syntax errors. Once compilation success then PVM (Python Virtual Machine) is responsible to execute.
9. Extensible:
We can use other language programs in Python. The main advantages of this approach are:
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
- We can use already existing legacy non-Python code
- We can improve performance of the application
10. Embedded:
We can use Python programs in any other language programs. i.e we can embedd Python programs anywhere.
11. Extensive Library:
Python has a rich inbuilt library. Being a programmer we can use this library directly and we are not responsible to implement the functionality. etc...
Limitations of Python:
- Performance wise not up to the mark b'z it is interpreted language.
- Not using for mobile Applications
Flavors of Python:
1.CPython: It is the standard flavor of Python. It can be used to work with C lanugage Applications
- Jython or JPython: It is for Java Applications. It can run on JVM
- IronPython: It is for C#.Net platform 4.PyPy: The main advantage of PyPy is performance will be improved because JIT compiler is available inside PVM. 5.RubyPython For Ruby Platforms
- AnacondaPython It is specially designed for handling large volume of data processing. ...
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Identifiers
A name in Python program is called identifier. It can be class name or function name or module name or variable name. a = 10
Rules to define identifiers in Python:
- The only allowed characters in Python are alphabet symbols(either lower case or upper case) digits(0 to 9) underscore symbol(_) By mistake if we are using any other symbol like $ then we will get syntax error. cash = 10 √ ca$h =20
- Identifier should not starts with digit 123total total123 √
- Identifiers are case sensitive. Of course Python language is case sensitive language. total= TOTAL= print(total) # print(TOTAL) #
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
Identifier:
Alphabet Symbols (Either Upper case OR Lower case)
If Identifier is start with Underscore (_) then it indicates it is private.
Identifier should not start with Digits.
Identifiers are case sensitive.
We cannot use reserved words as identifiers Eg: def=10
There is no length limit for Python identifiers. But not recommended to use too lengthy identifiers.
Dollor ($) Symbol is not allowed in Python.
Q. Which of the following are valid Python identifiers?
1 ) 123total 2 ) total123 √ 3 ) java2share √ 4 ) ca$h 5 ) abc_abc √ 6 ) def 7 ) if
Note:
- If identifier starts with _ symbol then it indicates that it is private
- If identifier starts with __(two under score symbols) indicating that strongly private identifier. 3.If the identifier starts and ends with two underscore symbols then the identifier is language defined special name,which is also known as magic methods. Eg: add
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, Data Types Data Type represent the type of data present inside a variable. In Python we are not required to specify the type explicitly. Based on value provided,the type will be assigned automatically.Hence Python is Dynamically Typed Language. Python contains the following inbuilt data types
- int
- float 3.complex 4.bool 5.str 6.bytes 7.bytearray 8.range 9.list 10.tuple 11.set 12.frozenset 13.dict 14.None Note: Python contains several inbuilt functions 1.type() to check the type of variable
- id() to get address of object 10 10 20 a a b a = 10 a = 20 a = 10 b = 10
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
- print() to print the value In Python everything is object
int data type:
We can use int data type to represent whole numbers (integral values) Eg: a= type(a) #int Note: In Python2 we have long data type to represent very large integral values. But in Python3 there is no long type explicitly and we can represent long values also by using int type only. We can represent int values in the following ways
- Decimal form
- Binary form
- Octal form
- Hexa decimal form
1. Decimal form(base-10):
It is the default number system in Python The allowed digits are: 0 to 9 Eg: a =
2. Binary form(Base-2):
The allowed digits are : 0 & 1 Literal value should be prefixed with 0b or 0B Eg: a = 0B a =0B a=b
3. Octal Form(Base-8):
The allowed digits are : 0 to 7 Literal value should be prefixed with 0o or 0O.
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, Eg: 1 ) >>> oct( 10 ) 2 ) '0o12' 3 ) >>> oct(0B1111) 4 ) '0o17' 5 ) >>> oct(0X123) 6 ) '0o443'
3. hex():
We can use hex() to convert from any base to hexa decimal Eg: 1 ) >>> hex( 100 ) 2 ) '0x64' 3 ) >>> hex(0B111111) 4 ) '0x3f' 5 ) >>> hex(0o12345) 6 ) '0x14e5'
float data type:
We can use float data type to represent floating point values (decimal values) Eg: f=1. type(f) float We can also represent floating point values by using exponential form (scientific notation) Eg: f=1.2e print(f) 1200. instead of 'e' we can use 'E' The main advantage of exponential form is we can represent big values in less memory. ***Note: We can represent int values in decimal, binary, octal and hexa decimal forms. But we can represent float values only by using decimal form. Eg: 1 ) >>> f=0B11. 01 2 ) File "", line 1 3 ) f=0B11. 01
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, 4 ) ^ 5 ) SyntaxError: invalid syntax 6 ) 7 ) >>> f=0o123. 456 8 ) SyntaxError: invalid syntax 9 ) 10 ) >>> f=0X123. 456 11 ) SyntaxError: invalid syntax
Complex Data Type:
A complex number is of the form a and b contain intergers or floating point values Eg: 3+5j 10+5.5j 0.5+0.1j In the real part if we use int value then we can specify that either by decimal,octal,binary or hexa decimal form. But imaginary part should be specified only by using decimal form. 1 ) >>> a=0B11+5j 2 ) >>> a 3 ) ( 3 +5j) 4 ) >>> a= 3 +0B11j 5 ) SyntaxError: invalid syntax Even we can perform operations on complex type values. 1 ) >>> a= 10 +1.5j 2 ) >>> b= 20 +2.5j 3 ) >>> c=a+b 4 ) >>> print(c) 5 ) ( 30 +4j) 6 ) >>> type(c) 7 ) <class 'complex'>
a + bj
Real Part Imaginary Part j2 = - 1 j =
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, soft" For this requirement we should go for triple single quotes(''') or triple double quotes(""") s1='''durga soft''' s1="""durga soft""" We can also use triple quotes to use single quote or double quote in our String. ''' This is " character''' ' This i " Character ' We can embed one string in another string '''This "Python class very helpful" for java students'''
Slicing of Strings:
slice means a piece [ ] operator is called slice operator,which can be used to retrieve parts of String. In Python Strings follows zero based index. The index can be either +ve or - ve. +ve index means forward direction from Left to Right
- ve index means backward direction from Right to Left 1 ) >>> s="durga" 2 ) >>> s[ 0 ] 3 ) 'd' 4 ) >>> s[ 1 ] 5 ) 'u' 6 ) >>> s[- 1 ] 7 ) 'a' 8 ) >>> s[ 40 ] IndexError: string index out of range d u r g a 0 1 2 3 4
- 5 - 4 - 3 - 2 - 1
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038, 1 ) >>> s[ 1 : 40 ] 2 ) 'urga' 3 ) >>> s[ 1 :] 4 ) 'urga' 5 ) >>> s[: 4 ] 6 ) 'durg' 7 ) >>> s[:] 8 ) 'durga' 9 ) >>> 10 ) 11 ) 12 ) >>> s* 3 13 ) 'durgadurgadurga' 14 ) 15 ) >>> len(s) 16 ) 5 Note:
- In Python the following data types are considered as Fundamental Data types int float complex bool str
- In Python,we can represent char values also by using str type and explicitly char type is not available. Eg: 1 ) >>> c='a' 2 ) >>> type(c) 3 ) <class 'str'>
- long Data Type is available in Python2 but not in Python3. In Python3 long values also we can represent by using int type only.
- In Python we can present char Value also by using str Type and explicitly char Type is not available.
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
2. float():
We can use float() function to convert other type values to float type. 1 ) >>> float( 10 ) 2 ) 10. 3 ) >>> float( 10 +5j) 4 ) TypeError: can't convert complex to float 5 ) >>> float(True) 6 ) 1. 7 ) >>> float(False) 8 ) 0. 9 ) >>> float("10") 10 ) 10. 11 ) >>> float("10.5") 12 ) 10. 13 ) >>> float("ten") 14 ) ValueError: could not convert string to float: 'ten' 15 ) >>> float("0B1111") 16 ) ValueError: could not convert string to float: '0B1111'
Note:
- We can convert any type value to float type except complex type.
- Whenever we are trying to convert str type to float type compulsary str should be either integral or floating point literal and should be specified only in base-10.
3.complex():
We can use complex() function to convert other types to complex type.
Form-1: complex(x)
We can use this function to convert x into complex number with real part x and imaginary part 0. Eg: 1 ) complex( 10 )==> 10 +0j 2 ) complex(10.5)===>10.5+0j 3 ) complex(True)==> 1 +0j 4 ) complex(False)==>0j 5 ) complex("10")==> 10 +0j 6 ) complex("10.5")==>10.5+0j 7 ) complex("ten") 8 ) ValueError: complex() arg is a malformed string
DURGASOFT, # 202, 2 nd^ Floor, HUDA Maitrivanam, Ameerpet, Hyderabad - 500038,
Form-2: complex(x,y)
We can use this method to convert x and y into complex number such that x will be real part and y will be imaginary part. Eg: complex(10,-2)==>10-2j complex(True,False)==>1+0j
4. bool():
We can use this function to convert other type values to bool type. Eg: 1 ) bool( 0 )==>False 2 ) bool( 1 )==>True 3 ) bool( 10 )===>True 4 ) bool(10.5)===>True 5 ) bool(0.178)==>True 6 ) bool(0.0)==>False 7 ) bool( 10 - 2j)==>True 8 ) bool( 0 +1.5j)==>True 9 ) bool( 0 +0j)==>False 10 ) bool("True")==>True 11 ) bool("False")==>True 12 ) bool("")==>False
