PYTHON -Chapter 2 - Functions, Exception, Modules and Files -MAULIK BORSANIYA

A function is a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing. Function Defining a Function You can define functions to provide the required functionality. Here are simple rules to define a function in Python. Function blocks begin with the keyword def followed by the function name and parentheses ( ( ) ). Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses. The code block within every function starts with a colon (:) and is indented. The statement return [expression] exits a function, Maulik Borsaniya - Gardividyapith

User Defining Function • Simple function def my_function(): print("Hello from a function") my_function() • Parameterized Function Def my_function(country = "Norway"): print("I am from " + country) my_function("Sweden") my_function("India") my_function() my_function("Brazil") • Return Value def my_function(x): return 5 * x print(my_function(3)) print(my_function(5)) print(my_function(9)) Maulik Borsaniya - Gardividyapith

Built In Function List of Built in function Maulik Borsaniya - Gardividyapith

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ABS() integer = -20 print('Absolute value of -20 is:',abs(integer)) Chr() print(chr(97)) print(chr(65)) Max & Min # using max(arg1, arg2, *args) print('Maximum is:', max(1, 3, 2, 10, 4)) # using min(iterable) num = [1, 3, 2, 8, 5, 10, 6] print('Maximum is:', min(num)) Maulik Borsaniya - Gardividyapith

Method • Python has some list methods that you can use to perform frequency occurring task (related to list) with ease. For example, if you want to add element to a list, you can use append() method. Simple Example animal = ['cat', 'dog', 'rabbit'] animal.append('pig') #Updated Animal List print('Updated animal list: ', animal) • Eg-1 Eg-2 numbers = [2.5, 3, 4, -5] numbersSum = sum(numbers) print(numbersSum) Maulik Borsaniya - Gardividyapith

Difference Between method and function Python Method • Method is called by its name, but it is associated to an object (dependent). • A method is implicitly passed the object on which it is invoked. • It may or may not return any data. • A method can operate on the data (instance variables) that is contained by the corresponding class Functions • Function is block of code that is also called by its name. (independent) • The function can have different parameters or may not have any at all. If any data (parameters) are passed, they are passed explicitly. • It may or may not return any data. • Function does not deal with Class and its instance concept. Maulik Borsaniya - Gardividyapith

# Basic Python method class class_name def method_name () : ...... # method body #Function Syntex def function_name ( arg1, arg2, ...) : ...... # function body ...... Maulik Borsaniya - Gardividyapith

Lambda • A lambda function is a small anonymous function. • A lambda function can take any number of arguments, but can only have one expression. Syntax • lambda arguments : expression • Eg.1 x = lambda a : a + 10 print(x(5)) • Eg.2 x = lambda a, b : a * b print(x(5, 6)) Maulik Borsaniya - Gardividyapith

Why Use Lambda Functions? The power of lambda is better shown when you use them as an anonymous function inside another function. Say you have a function definition that takes one argument, and that argument will be multiplied with an unknown number. • Eg. def myfunc(n): return lambda a : a * n mydoubler = myfunc(2) print(mydoubler(11)) print(mydoubler(10)) Maulik Borsaniya - Gardividyapith

Filter With Lambda • The filter() function in Python takes in a function and a list as arguments. • The function is called with all the items in the list and a new list is returned which contains items for which the function evaluates to True. • Here is an example use of filter() function to filter out only even numbers from a list. • Eg.1 my_list = [1, 5, 4, 6, 8, 11, 3, 12] new_list = list(filter(lambda x: (x%2 == 0) , my_list)) print(new_list) Maulik Borsaniya - Gardividyapith

Map With Lambda • The map() function in Python takes in a function and a list. • The function is called with all the items in the list and a new list is returned which contains items returned by that function for each item. • Here is an example use of map() function to double all the items in a list. • Eg.1 my_list = [1, 5, 4, 6, 8, 11, 3, 12] new_list = list(map(lambda x: x * 2 , my_list)) print(new_list) Maulik Borsaniya - Gardividyapith

Creating our own module 1) Hello.py # Define a function def world(): print("Hello, World!") 2) Main.py # Import hello module import hello # Call function hello.world()  print(hello.variable)  variable = "Sammy" Maulik Borsaniya - Gardividyapith

Exception Handling • An exception is an event, which occurs during the execution of a program that disrupts the normal flow of the program's instructions. In general, when a Python script encounters a situation that it cannot cope with, it raises an exception. An exception is a Python object that represents an error. • When a Python script raises an exception, it must either handle the exception immediately otherwise it terminates and quits.(there are many built in exception is there)Maulik Borsaniya - Gardividyapith

Syntax try: You do your operations here; ...................... except Exception 1: If there is Exception 1, then execute this block. ……………………. except Exception 2: If there is Exception 2, then execute this block. ...................... else: If there is no exception then execute this block. finally : This would always be executed Maulik Borsaniya - Gardividyapith

• Example try: fh = open("asd.txt", "w") fh.write("This is my test file for exception handling!!") except IOError: print "Error: can't find file or read data" else: print "Written content in the file successfully" fh.close() Finally: Print “wow Yaar !! You wrotted hainn !” Maulik Borsaniya - Gardividyapith

Exception Handling With Assert Statement • Syntex : assert expression, argument, messag Eg . assert 2 + 2 == 4 assert 2 + 3 == 3, ’’error is here’’ Eg.2 def avg(marks): assert len(marks) != 0,"List is empty.“ return sum(marks)/len(marks) mark2 = [55,88,78,90,79] print("Average of mark2:",avg(mark2)) mark1 = [] print("Average of mark1:",avg(mark1)) • Python has built-in assert statement to use assertion condition in the program. • assert statement has a condition or expression which is supposed to be always true. • If the condition is false assert halts the program and gives an AssertionError. Maulik Borsaniya - Gardividyapith

User Define Exception class Error(Exception): """Base class for other exceptions""" pass class ValueTooSmallError(Error): """Raised when the input value is too small""" pass class ValueTooLargeError(Error): """Raised when the input value is too large""" pass # our main program # user guesses a number until he/she gets it right # you need to guess this number number = 10 while True: try: i_num = int(input("Enter a number: ")) if i_num < number: raise ValueTooSmallError elif i_num > number: raise ValueTooLargeError break except ValueTooSmallError: print("This value is too small, try again!") print() except ValueTooLargeError: print("This value is too large, try again!") print() print("Congratulations! You guessed it correctly.") Maulik Borsaniya - Gardividyapith

• File Handling The key function for working with files in Python is the open() function. The open() function takes two parameters; filename, and mode. There are four different methods (modes) for opening a file: • "r" - Read - Default value. Opens a file for reading, error if the file does not exist • "a" - Append - Opens a file for appending, creates the file if it does not exist • "w" - Write - Opens a file for writing, creates the file if it does not exist • "x" - Create - Creates the specified file, returns an error if the file exists Maulik Borsaniya - Gardividyapith

DemoFile.txt • Hello! Welcome to demofile.txt This file is for testing purposes. Good Luck! Python file read  f = open("demofile.txt", "r") print(f.read()) #print(f.readline()) append  f = open("demofile.txt", "a") f.write("Now the file has one more line!") Write  f = open("demofile.txt", "w") f.write("Woops! I have deleted the content!") Maulik Borsaniya - Gardividyapith

Remove file import os if os.path.exists(“demofile"): os.remove(“demofile") else: print("The file does not exist") Maulik Borsaniya - Gardividyapith

File Positions • The tell() method tells you the current position within the file; in other words, the next read or write will occur at that many bytes from the beginning of the file. • The seek(offset[, from]) method changes the current file position. The offset argument indicates the number of bytes to be moved. The from argument specifies the reference position from where the bytes are to be moved. • If from is set to 0, it means use the beginning of the file as the reference position and 1 means use the current position as the reference position and if it is set to 2 then the end of the file would be taken as the reference position. Maulik Borsaniya - Gardividyapith

• # Open a file fo = open("foo.txt", "r+") str = fo.read(10); print "Read String is : ", str # Check current position position = fo.tell(); print "Current file position : ", position # Reposition pointer at the beginning once again position = fo.seek(0, 0); str = fo.read(10); print "Again read String is : ", str # Close opend file fo.close() Maulik Borsaniya - Gardividyapith

Sr.No. Modes & Description 1 r Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode. 2 rb Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode. 3 r+ Opens a file for both reading and writing. The file pointer placed at the beginning of the file. 4 rb+ Opens a file for both reading and writing in binary format. The file pointer placed at the beginning of the file. 5 w Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing. Maulik Borsaniya - Gardividyapith

6 wb Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing. 7 w+ Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. 8 wb+ Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. 9 a Opens a file for appending. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. 10 ab Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. 11 a+ Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. 12 ab+ Opens a file for both appending and reading in binary format. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. Maulik Borsaniya - Gardividyapith

Running Other Programs from Python Program – Windows python • import os • command = "cmd" • os.system(command) Maulik Borsaniya - Gardividyapith

Python For Loops • A for loop is used for iterating over a sequence (that is either a list, a tuple or a string). • This is less like the for keyword in other programming language, and works more like an iterator method as found in other object-orientated programming languages. • With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc. Example • fruits = ["apple", "banana", "cherry"] for x in fruits: print(x) Maulik Borsaniya - Gardividyapith

• fruits = ["apple", "banana", "cherry"] for x in fruits: if x == "banana": break print(x) • for x in range(2, 30, 3): print(x) • i = 1 while i < 6: print(i) i += 1 Maulik Borsaniya - Gardividyapith

PYTHON -Chapter 2 - Functions, Exception, Modules and Files -MAULIK BORSANIYA

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PYTHON -Chapter 2 - Functions, Exception, Modules and Files -MAULIK BORSANIYA