Python programming: Anonymous functions, String operations

Python Programming
Part V
Megha V
Research Scholar
Kannur University
09-11-2021 meghav@kannuruniv.ac.in 1

Anonymous Functions
• Anonymous function is a function that is defined without a name.
• Anonymous function is defined using the lambda keyword
• Also called lambda functions
syntax
lambda [,arg1 [,arg2,……….argn]]:expression
Eg: # Lambda function definition
square=lambda x : x*x;
# Usage of lambda function
n=int(input(“Enter a number:”))
print(“square of”,n,”is”,square(n)) #
Output
Enter a number:5
Square of 5 is 25

Main characteristics of lambda function
1. Lambda functions can take any number of arguments but return only one
value in the form of an expression
2. It cannot contain multiple expressions
3. It cannot have comments
4. A lambda function cannot be a direct call to print because lambda requires
an expression
5. Lambda functions have their own local namespace and cannot access
variables other than those in their parameter list and those in the global
namespace
6. Lambda functions are not equivalent to inline functions in C or C++

• lambda is the keyword, x shows the argument passed, and x*x is the
expression to be evaluated and stored in the variable square
Example with two arguments
# Lambda function definition
sum =lambda x,y : x+y
#usage of lambda function
m=int(input(“Enter first number:”))
n=int(input(“Enter second number:”))
print(“sum of”,m,”and”,n,”is”,sum(m,n))#lambda function call

Use of lambda function
• We use lambda function when we require a nameless function for a
short period of time.
• Lambda functions are used along with built-in functions like filter(),
map() etc
• The map() function in Python takes input; function and a list.
• The function is called with all the item in the list and a new list is
returned which contains items returned by that function for each
item

#Lambda function to increment the items in list by 2
oldlist=[2,31,42,11,6,5,23,44]
print(oldlist)
#Usage of lambda function
newlist=list(map(lambda x: x+2,oldlist))
print(“List after incrementation by 2”)
print(newlist)
Output
[2,31,42,11,6,5,23,44]
List after incrementation by 2
[4,33,44,13,8,7,25,46]
lambda function

• filter() function
• The function filter(function,list) offers a way to filter out all the elements
of a list, for which the function returns True.
• The first argument function returns a Boolean value, i.e., either True or
False.
• This function will be applied to every element of the list lis.

Example: The function called with all the items in the list and a new list is returned
which contains items for which the function evaluates to True
#Lambda function to filter out only odd numbers from a
list
oldlist=[2,31,42,11,6,5,23,44]
newlist=list(filter(lambda x:(x%2!=0),oldlist))
print(oldlist)
print(newlist)
Output
[2,31,42,11,6,5,23,44]
[31,11,5,23]

reduce() function
• The function reduce(func,seq) continually applies the fuction func() to the
sequence seq.
• It returns a single value
• If seq=[s1,s2, s3…………….sn], calling reduce(func,seq) work like this:
• At first the two elements of seq will be applied to func, i.e func(s1,s2)
• The list on which reduce() works looks now like this: [func(s1,s2),s3………sn]
• In the next step func will be applied on the previous result and the third
element of the list, i.e. func(func(s1,s2),s3)
• The list looks like this now: [func(func(s1,s2),s3),………,sn]

• Continue like this until just one element is left and return this element as the
result of reduce()
• Used for performing some computation on list and returning the result.
• The following example illustrates the use of reduce() function, that computes
the product of a list of integers
• Example:
import functools
list=[1,2,3,4]
product=functools.reduce[lambda x,y:x*y,list]
print(list)
print(“Product=” product)
Output
[1,2,3,4]
product=24

Function with more than one return type
• Instead of writing separate functions for returning individual values, we can return all the values withing
same function
• Example: def cal(a,b)
sum=a+b
diff=a-b
prod=a*b
quotient=a/b
return sum,diff,prod,quotient
a=int(input(“Enter first number:”))
b=int(input(“Enter second number:”))
s,d,p,q=calc(a,b)
print(“Sum=”,s)
print(“Difference=”,d)
print(“Product=”,p)
print(“Quotient=”,q)
Output
Enter first number:10
Enter Second number:5
Sum=15
Difference=5
Product=50
Quotient=5

Strings
• Python allows several string operators that can be applied on the python
string are as below:
1. Assignment operator: “=.”
2. Concatenate operator: “+.”
3. String repetition operator: “*.”
4. String slicing operator: “[]”
5. String comparison operator: “==” & “!=”
6. Membership operator: “in” & “not in”
7. Escape sequence operator: “.”
8. String formatting operator: “%” & “{}”

Basic String operations
• Assignment operator: “=.”
string1 = "hello“
• Concatenate operator: “+.”
string1 = "hello"
string2 = "world "
string_combined = string1+string2
print(string_combined)
• String repetition operator: “*.”
string1 = "helloworld "
print(string1*2)

string1 = "helloworld"
print(string1[1])
print(string1[-3])
print(string1[1:5])
print(string1[1:-3])
print(string1[2:])
print(string1[:5])
print(string1[:-2])
print(string1[-2:])
print(string1[::-1])
• String slicing operator: “[]”

String comparison operator: “==” & “!=”
string1 = "hello"
string2 = "hello, world"
string3 = "hello, world"
string4 = "world"
print(string1==string4) #False
print(string2==string3) #True
print(string1!=string4) #True
Membership operator: “in” & “not in”
string1 = "helloworld"
print("w" in string1) #True
print("W" in string1) #False
print("t" in string1) #False
print("t" not in string1) #True
print("hello" in string1) #True
print("Hello" in string1) #False

• EscapeSequence Operator“.”
• To inserta non-allowedcharacterin thegiveninput string,an escapecharacterisused.
• An escapecharacterisa “” or “backslash”operatorfollowedby a non-allowedcharacter.
string = "Hello world I am from "India""
print(string) #ERROR
string = "Hello world I am from "India""
print(string)
Output
Hello world I am from “India”

• Escape characters
• An escape character is a character that gets interpreted when placed
in single or double quotes
Escape character Description
a Bell or alert
b Backspace
f Formfeed
n Newline
r Carriage return
s Space
t Tab
v Vertical Tab

• String formatting operator: “%” & “{}”
• String formatting operator is used to format a string as per requirement
name = "india"
age = 19
marks = 20.56
string1 = 'Hey %s' % (name)
print(string1)
string2 = 'my age is %d' % (age)
print(string2)
string3= 'Hey %s, my age is %d' % (name, age)
print(string3)
string3= 'Hey %s, my subject mark is %f' % (name, marks)
print(string3)
Operator Description
%d Signed decimal integer
%u unsigned decimal integer
%c Character
%s String
%f Floating-point real number

Strings
• Python has a set of built-in methods that you can use on strings.
Method Description
capitalize() Converts the first character to upper case
casefold() Converts string into lower case
center() Returns a centered string
count() Returns the number of times a specified value occurs in a string
encode() Returns an encoded version of the string
endswith() Returns true if the string ends with the specified value
expandtabs() Sets the tab size of the string
find() Searches the string for a specified value and returns the position of where it was found
format() Formats specified values in a string
format_map() Formats specified values in a string
index() Searches the string for a specified value and returns the position of where it was found
isalnum() Returns True if all characters in the string are alphanumeric
isalpha() Returns True if all characters in the string are in the alphabet
isascii() Returns True if all characters in the string are ascii characters

isdecimal() Returns True if all characters in the string are decimals
isdigit() Returns True if all characters in the string are digits
isidentifier() Returns True if the string is an identifier
islower() Returns True if all characters in the string are lower case
isnumeric() Returns True if all characters in the string are numeric
isprintable() Returns True if all characters in the string are printable
isspace() Returns True if all characters in the string are whitespaces
istitle() Returns True if the string follows the rules of a title
isupper() Returns True if all characters in the string are upper case
join() Converts the elements of an iterable into a string
ljust() Returns a left justified version of the string
lower() Converts a string into lower case

lstrip() Returns a left trim version of the string
maketrans() Returns a translation table to be used in translations
partition() Returns a tuple where the string is parted into three parts
replace() Returns a string where a specified value is replaced with a specified value
rfind() Searches the string for a specified value and returns the last position of where it was found
rindex() Searches the string for a specified value and returns the last position of where it was found
rjust() Returns a right justified version of the string
rpartition() Returns a tuple where the string is parted into three parts
rsplit() Splits the string at the specified separator, and returns a list
rstrip() Returns a right trim version of the string
split() Splits the string at the specified separator, and returns a list

splitlines() Splits the string at line breaks and returns a list
startswith() Returns true if the string starts with the specified value
strip() Returns a trimmed version of the string
swapcase() Swaps cases, lower case becomes upper case and vice
versa
title() Converts the first character of each word to upper case
translate() Returns a translated string
upper() Converts a string into upper case
zfill() Fills the string with a specified number of 0 values at
the beginning

Example
s=‘Learning Python is easy’
print(s.lower())
print(s.title())
print(s.upper())
print(s.swapcase())
print(s.capitalize())

Python programming: Anonymous functions, String operations

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