Networking And Scripting : Python String & String Programs

Strings in Python:

=============

Strings are immutable sequence of characters.

Python accepts single, double and triple quotes.

There are actually 3 ways to define a string using either single, double or triple quotes:

text = 'The surface of the circle is 2 pi R = '

text = "The surface of the circle is 2 pi R = "

text = '''The surface of the circle is 2 pi R = '''

text = """The surface of the circle is 2 pi R = """

NOTE:

· Strings in double quotes work exactly the same as in single quotes but allow to insert single quote character inside them.

· The interest of the triple quotes (‘’’ or “””) is that you can specify multi-line strings.

· Moreover, single quotes and double quotes can be used freely within the triple quotes:

""" a string with special character " and ' inside """

· The ” and ‘ characters are part of the Python language; they are special characters. To insert them in a string, you have to escape them (i.e., with a \ chracter in front of them to indicate the special nature of the character). For instance:

text = " a string with escaped special character \", \' inside "

· To include unicode, you must precede the string with the u character:

>>> u"\u0041"

unicode is a single character set used to represent 65536 different characters.

String input and output:
To output text (string) to the screen:
s = "hello world"
print(s)

To get text from keyboard:

[Python 3.x]
name = input("Enter name: ")
print(name)

[Python 2.x]
name = raw_input("Enter name: ")
print(name)

String Formatter:

In Python, the % sign lets you produce formatted output.

A quick example will illustrate how to print a formatted string:

>>> print("%s" % "some text")

"some text"

The syntax is simply:

string % values

If you have more than one value, they should be placed within brackets:

>>> print("%s %s" % ("a", "b"))

The string contains characters and conversion specifiers (here %s)

To escape the sign %, just double it:

>>> print "This is a percent sign: %%"

This is a percent sign:

String Operators:

The mathematical operators + and * can be used to create new strings:

t = 'This is a test'

t2 = t+t

t3 = t*3

and comparison operators >, >=, ==, <=, < and != can be used to compare strings.

String Comparison:
To test if two strings are equal use the equality operator (==).

#!/usr/bin/python
sentence = "The cat is brown"
q = "cat"
if q == sentence:
print('strings equal')

To test if two strings are not equal use the inequality operator (!=)
#!/usr/bin/python
sentence = "The cat is brown"
q = "cat"
if q != sentence:
print('strings equal')

String Index
Python indexes the characters of a string, every index is associated with a unique character. For instance, the characters in the string ‘python’ have indices:
String
String numbering
Characters in string

The 0th index is used for the first character of a string.

Try the following:

#!/usr/bin/python
s = "Hello Python"
print(s) # prints whole string
print(s[0]) # prints "H"
print(s[1]) # prints "e"

String Slicing:
Given a string s, the syntax for a slice is:
s[ startIndex : pastIndex ]
The startIndex is the start index of the string. pastIndex is one past the end of the slice.
NOTE:

If you omit the first index, the slice will start from the beginning. If you omit the last index, the slice will go to the end of the string. For instance:

#!/usr/bin/python
s = "Hello Python"
print(s[0:2]) # prints "He"
print(s[2:4]) # prints "ll"
print(s[6:]) # prints "Python"

Example:

=======

foo = "Monty Python's Flying Circus"

#Print the middle of foo- slice from the 7th-1 character end at the 15th-1 character

print foo[6:14]

#Use a slice to get the first six characters

print foo[:6]

#>>> Monty

#Slice after the first six characters of foo

print foo[6:]

#>>> Python's Flying Circus

#Print everthing in foo

print foo[:]

#>>> Monty Python's Flying Circus

#Every second character

print foo[0:27:2]

#>>> MnyPto' ligCru

#The last character of foo

print foo[-1]

#>>> s

#The last two characters of foo

print foo[-2:]

#>>> us

#Everything but the last seven charachers of foo

print foo[:-7]

#>>> Monty Python's Flying

Split() and Join() Methods in Python?

Split() - Returns a list by seperating the elements based on the delimiter. (Returns List)
-------
Example:
testString = "This,is,the,test,string"
testString.split(',')

Output:
['This', 'is', 'the', 'test', 'string']
Join()
------
str.Join() - Method returns a string This method returns a string.
Which is the concatenation of the strings in the sequence seq.
The separator between elements is the string providing this method.

e.x:
"".join(testString)

Output-> 'This,is,the,test,string'

e.x:
"-".join(testString)
Output-> 'T-h-i-s-,-i-s-,-t-h-e-,-t-e-s-t-,-s-t-r-i-n-g'

String-class:-
==========
>>default is UNICODE strings
>>single quoted    a='hello'
>>double quoted a="hello"
>>triple quoted     a='''hello'''

Convert the string from UNICODE to bytes
a="hello" # Str
res=a.encode("utf-8") # converts unicode string to bytes
ALITER
a=b"Hello" # bytes
hardware representation is in bytes

a=b"hello"
res=a.decode("utf-8") # convert bytes to UNICODE STRING

String operations:-
a='hello world'
string length            : len(a)
first element            : a[0] # indexing
last element           : a[-1]
first 4 elems            : a[:4] # slicing
last 4 elems           : a[-4:]
except first 4           : a[4:]
except last 4            : a[:-4]
except first 4 & last 4      : a[4:-4]
Alt elem            : a[::2]
Alt elem             : a[1::2]
reverse             : a[::-1]
concate           : "hello" + a
upper              : a.upper()

Ex: Accept the string from the user as “sampling” and print as

sa-MPLI-ng
Sol:

res = input("Enter the string : ")
new = res[:2]+"-"+res[2:-2].upper()+"-"+res[-2:]
print(new)

Ex: Accept the string from the user as “sampling” and print as

S-nilpma-G
Sol:
res[0].upper() + "-" + res[1:-1][::-1].lower() + "-" + res[-1].upper()

Others functions:-
Search for a substring in a string ---->

"hello" in mystr
----> "hello" not in mystr
split the string -----> flst = a.split(delimiter)

a="192.168.1.125"

>> is "a" is string var - YES
>> what is delimiter - "."
flst = a.split(".")
print(flst)
print(len(flst))
print(flst[0])
print(flst[-1])

find:-
------------
a.replace()
a.count()
a.index()
a.rindex()
a.find()
a.rfind()
a.rstrip()
a.lstrip()
a.strip()

----------------------------------------------------------------
a='sample data was added'

display the first word a.split()[0]
display the last word a.split()[-1]

display the first words last char a.split()[0][-1]
display the last words first char a.split()[-1][0]

a=10 20 30 40 50 60 70"
display first 4 fields

a.split()[0:4]

a="north 10,20,30,40"
display the first & last fields i.e 10 & 40

flst = a.split()[1].split(",")
print(flst[0],flst[-1])

import re
a="north 10,20,30,40"
flst = re.split("[\s,]",a)
ALITER
import re
a="sample-----hello-data----using-done"
b=re.sub("-+","-",a)
print(a)

a="north 10,20,30,40"

Things To Remember:

=================

1. How to convert a string to an int in python?
int(x [,base]) - Converts x to an integer. base specifies the base if x is a string.

2.How to convert a string to a long in python?
long(x [,base] ) - Converts x to a long integer. base specifies the base if x is a string.

3..How to convert a string to a float in python?
float(x) − Converts x to a floating-point number.

4.How will you convert a object to a string in python?
str(x) − Converts object x to a string representation.

5.How to convert a String to an object in python?
eval(str) − Evaluates a string and returns an object.

6.How to convert a string to a tuple in python?
tuple(s) − Converts s to a tuple.

7.How to convert a string to a list in python?
list(s) − Converts s to a list.

8.How to convert a string to a set in python?
set(s) − Converts s to a set.

9.How to convert an integer to hexadecimal string in python?
hex(x) − Converts an integer to a hexadecimal string.

10.How to capitalizes first letter of string?
capitalize() − Capitalizes first letter of string.

11.How to check in a string that all characters are digits?
isdigit() − Returns true if string contains only digits and false otherwise.

12.How to check in a string that all characters are alphanumeric?
isalnum() − Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise.

13.How to check in a string that all characters are in lowercase?
islower() − Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise.

14.How to check in a string that all characters are numerics?
isnumeric() − Returns true if a unicode string contains only numeric characters and false otherwise.

15.How to check in a string that all characters are whitespaces?
isspace() − Returns true if string contains only whitespace characters and false otherwise.

16.How to check in a string that it is properly titlecased?
istitle() − Returns true if string is properly "titlecased" and false otherwise.

17.How to check in a string that all characters are in uppercase?
isupper() − Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise.

18.How will you get the length of the string?
len(string) − Returns the length of the string.

19.How will you remove all leading whitespace in string?
lstrip() − Removes all leading whitespace in string.

20.How to replaces all occurrences of old substring in string with new string?
replace(old, new [, max]) − Replaces all occurrences of old in string with new or at most max occurrences if max given.

21.How to remove all leading and trailing whitespace in string?
strip([chars]) − Performs both lstrip() and rstrip() on string.

22.How to get titlecased version of string?
title() − Returns "titlecased" version of string, that is, all words begin with uppercase and the rest are lowercase.

23. split(), sub(), subn() methods :
To modify the strings, Python’s “re” module is providing 3 methods. They are:
split() – uses a regex pattern to “split” a given string into a list.
sub() – finds all substrings where the regex pattern matches and then replace them with a different string
subn() – it is similar to sub() and also returns the new string along with the no. of
replacements.

24.Methods for matching and searching the occurrences of a pattern in a given text String ?
There are 4 different methods in “re” module to perform pattern matching. They are:
match() – matches the pattern only to the beginning of the String. search() – scan the string and look for a location the pattern matches findall() – finds all the occurrences of match and return them as a list
finditer() – finds all the occurrences of match and return them as an iterator.

String Related Programs:

===================

1. Find the sum of two numbers
a = input ("Enter the value of a : ")
b = input ("Enter the value of b : ")
#Note :By defult input takes a string
res = int(a) + int(b)
print("Final ans = ", res)

2. Remove the whitespaces from the string.
s = ‘aaa bbb ccc ddd eee’
''.join(s.split())

3. Write a Python program to check for a number at the end of a string

import re

def end_num(string):

text = re.compile(r".*[0-9]$")

if text.match(string):

return True

else:

return False

print(end_num('abcdef'))

print(end_num('abcdef6'))

4. Write a Python program to find the substrings within a string

import re

text = 'Python exercises, PHP exercises, C# exercises'

pattern = 'exercises'

for match in re.findall(pattern, text):

print('Found "%s"' % match)

5. Write a Python program to find the occurrence and position of the substrings within a string

import re

text = 'Python exercises, PHP exercises, C# exercises'

pattern = 'exercises'

for match in re.finditer(pattern, text):

s = match.start()

e = match.end()

print('Found "%s" at %d:%d' % (text[s:e], s, e))

6.Write a Python program to match if two words from a list of words starting with letter 'P'.

import re

# Sample strings.

words = ["Python PHP", "Java JavaScript", "c c++"]

for w in words:

m = re.match("(P\w+)\W(P\w+)", w)

# Check for success

if m:

print(m.groups())

7. Write a Python program to separate and print the numbers of a given string

import re

# Sample string.

text = "Ten 10, Twenty 20, Thirty 30"

result = re.split("\D+", text)

# Print results.

for element in result:

print(element)

8. Write a Python program to find all words starting with 'a' or 'e' in a given string

import re

# Input.

text = "The following example creates an ArrayList with a capacity of 50 elements. Four elements are then added to the ArrayList and the ArrayList is trimmed accordingly."

#find all the words starting with ‘a’ or ‘e’

list = re.findall("[ae]\w+", text)

# Print result.

print(list)

9. Write a Python program to separate and print the numbers and their position of a given string.

import re

# Input.

text = "The following example creates an ArrayList with a capacity of 50 elements. Four elements are then added to the ArrayList and the ArrayList is trimmed accordingly."

for m in re.finditer("\d+", text):

print(m.group(0))

print("Index position:", m.start())

10. Write a Python program to remove multiple spaces in a string

import re

text1 = 'Python Exercises'

print("Original string:",text1)

print("Without extra spaces:",re.sub(' +',' ',text1))

11.Write a Python program to remove all whitespaces from a string

import re

text1 = ' Python Exercises '

print("Original string:",text1)

print("Without extra spaces:",re.sub(r'\s+', '',text1))

12. DocStrings

What is docstring in Python?
A Python documentation string is known as docstring, it is a way of documenting Python functions, modules and classes.

docstring is the documentation string for a function. It can be accessed by

function_name.__doc__

it is declared as:
def function_name():
"""your docstring"""
Writing documentation for your progams is a good habit and makes the code more understandable and reusable.

def printMax(x,y):
'''print the maximum of two numbers.
The two values must be integers..'''
x = int(x)
y = int(y)

if x > y:
print(x, 'is maximum')
else:
print(y, 'is maximum')

printMax(3,5)
print(printMax.__doc__)

13. Strings
name = 'manish'
if name.startswith('man'):
print('Yes, the string starts with "man"')
if 'a' in name:
print('Yes, it contains the string "a"')
if name.find('ish') != -1:
print('Yes, it contains the string "ish"')
delimiter = '_*_'
mylist = ['USA','UK', 'India', 'Nepal']
print(delimiter.join(mylist))

14. Find if given string is palindrome
name = input("Enter the string: ")
if name[::] == name[::-1]:
print(name, "is a palindrome")
else:
print(name, "is not a palindrome")

15. Write a Python program that accepts a string and calculate the number of digits and letters

data = "Python 3.2"

d=l=0

for i in data:

if i.isdigit():

d += 1

elif i.isalpha():

l += 1

else:

pass

print("letters: ", l)

print("digits: ", d)

16. Write a Python program to reverse a string

def rev(str):

res = str[::-1]

return res

str = "1234abcd"

print(rev(str))

17.Write a Python function that accepts a string and calculate the number of upper case letters and lower case letters

def string_test(s):

d={"UPPER_CASE":0, "LOWER_CASE":0}

for c in s:

if c.isupper():

d["UPPER_CASE"] += 1

elif c.islower():

d["LOWER_CASE"] += 1

else:

pass

print("No of upper case chars: ", d["UPPER_CASE"])

print("NO of lower case chars:", d["LOWER_CASE"])

string_test('The quick Brown Fox')

18. Multiline in python
s = '''This is a multi-line string.
This is the second line...'''
print(s)

s = 'This is a string. \
This continues the string.'
print(s)
#ALITER
print\
(s)

19. What does the below mean?
s = a + ‘[‘ + b + ‘:’ + c + ‘]’
seems like a string is being concatenated. Nothing much can be said without knowing types of variables a, b, c. Also, if all of the a, b, c are not of type string, TypeError would be raised. This is because of the string constants (‘[‘ , ‘]’) used in the statement.

20.What would the following code yield?
word = 'abcdefghij'
print word[:3] + word[3:]

Ans: ‘abcdefghij’ will be printed.
This is called string slicing. Since here the indices of the two slices are colliding, the string slices are ‘abc’ and ‘defghij’. The ‘+’ operator on strings concatenates them. Thus, the two slices formed are concatenated to give the answer ‘abcdefghij’.

21. Program to Replace all Occurrences of ‘a’ with $ in a String:

string=input("Enter string:")

string=string.replace('a','$')

string=string.replace('A','$')

print("Modified string:")

print(string)

22. Program to Remove the nth Index Character from a Non-Empty String

def remove(string, n):

first = string[:n]

last = string[n+1:]

return first + last

string=input("Enter the sring:")

n=int(input("Enter the index of the character to remove:"))

print("Modified string:")

print(remove(string, n))

23. Program to Detect if Two Strings are Anagrams:

"An anagram is a type of word, the result of rearranging the letters of a word or phrase to produce a new word or phrase, using all the original letters exactly once. For example: orchestra can be rearranged into carthorse or cat can be rearranged into act.

s1=input("Enter first string:")

s2=input("Enter second string:")

if(sorted(s1)==sorted(s2)):

print("The strings are anagrams.")

else:

print("The strings aren't anagrams.")

Output:

Enter first string:anagram

Enter second string:nagaram

The strings are anagrams.

Enter first string:hello

Enter second string:world

The strings aren't anagrams.

24. Program to Form a New String where the First Character and the Last Character have been Exchanged

def change(string):

return string[-1:] + string[1:-1] + string[:1]

string=input("Enter string:")

print("Modified string:")

print(change(string))

Output:

Case 1:

Enter string:abcd

Modified string:

dbca

25.Program to Count the Number of Vowels in a String.

string=input("Enter string:")

vowels=0

for i in string:

if(i=='a' or i=='e' or i=='i' or i=='o' or i=='u' or i=='A' or i=='E' or i=='I' or i=='O' or i=='U'):

vowels=vowels+1

print("Number of vowels are:")

print(vowels)

26.Program to Take in a String and Replace Every Blank Space with Hyphen

string=input("Enter string:")

string=string.replace(' ','-')

print("Modified string:")

print(string)

Output:

Enter string:hello world

Modified string:

hello-world

Enter string:apple orange banana

Modified string:

apple-orange-banana

27. Program to Calculate the Length of a String Without Using a Library Function

string=input("Enter string:")

count=0

for i in string:

count=count+1

print("Length of the string is:")

print(count)

28.Program to Remove the Characters of Odd Index Values in a String

def modify(string):

final = ""

for i in range(len(string)):

if i % 2 == 0:

final = final + string[i]

return final

string=input("Enter string:")

print("Modified string is:")

print(modify(string))

Output:

Enter string:hello

Modified string is:

hlo

Enter string:checking

Modified string is:

cekn

29.Program to Calculate the Number of Words and the Number of Characters Present in a String

string=input("Enter string:")

char=0

word=1

for i in string:

char=char+1

if(i==' '):

word=word+1

print("Number of words in the string:")

print(word)

print("Number of characters in the string:")

print(char)

Output:

Enter string:Hello world

Number of words in the string:

Number of characters in the string:

Enter string:I love python

Number of words in the string:

Number of characters in the string:

3. Enter string: abcdef abcdef manish bidsar

Number of words in the string:

Number of characters in the string:

30.Program to Take in Two Strings and Display the Larger String without Using Built-in Functions

string1=input("Enter first string:")

string2=input("Enter second string:")

count1=0

count2=0

for i in string1:

count1=count1+1

for j in string2:

count2=count2+1

if(count1<count2):

print("Larger string is:")

print(string2)

elif(count1==count2):

print("Both strings are equal.")

else:

print("Larger string is:")

print(string1)

Output:

Enter first string:Bangalore

Enter second string:Delhi

Larger string is:

Bangalore

Enter first string: manish

Enter second string: abc

Larger string is:

Manish

31. Program to Count Number of Lowercase Characters in a String

string=input("Enter string:")

count=0

for i in string:

if(i.islower()):

count=count+1

print("The number of lowercase characters is:")

print(count)

Output:

Enter string:Hello

The number of lowercase characters is:

Enter string:AbCd

The number of lowercase characters is:

32.Program to Check if a String is a Palindrome or Not

string=input("Enter string:")

if(string==string[::-1]):

print("The string is a palindrome")

else:

print("The string isn't a palindrome")

Output:

Enter string:malayalam

The string is a palindrome

Enter string:manish

The string isn't a palindrome

33.Program to Calculate the Number of Upper Case Letters and Lower Case Letters in a String

string=input("Enter string:")

count1=0

count2=0

for i in string:

if(i.islower()):

count1=count1+1

elif(i.isupper()):

count2=count2+1

print("The number of lowercase characters is:")

print(count1)

print("The number of uppercase characters is:")

print(count2)

Output:

Enter string: Manish Bidsar

The number of lowercase characters is:

The number of uppercase characters is:

Enter string:HeLLo

The number of lowercase characters is:

The number of uppercase characters is:

34.Program to Check if a String is a Pangram or Not

from string import ascii_lowercase as asc_lower

def check(s):

return set(asc_lower) - set(s.lower()) == set([])

strng=raw_input("Enter string:")

if(check(strng)==True):

print("The string is a pangram")

else:

print("The string isn't a pangram")

Output:

Enter string:The quick brown fox jumps over the lazy dog

The string is a pangram

Enter string:Hello world

The string isn't a pangram

35.Program to Accept a Hyphen Separated Sequence of Words as Input and Print the Words in a Hyphen-Separated Sequence after Sorting them Alphabetically

print("Enter a hyphen separated sequence of words:")

lst=[n for n in input().split('-')]

lst.sort()

print("Sorted:")

print('-'.join(lst))

Output:

red-green-blue-yellow

Sorted:

blue-green-red-yellow

Enter a hyphen separated sequence of words:

Bangalore-hyderabad-delhi

Sorted:

Bangalore-delhi-hyderabad

36.Program to Calculate the Number of Digits and Letters in a String.

string=input("Enter string:")

count1=0

count2=0

for i in string:

if(i.isdigit()):

count1=count1+1

count2=count2+1

print("The number of digits is:")

print(count1)

print("The number of characters is:")

print(count2)

Output:

Enter string:Hello123

The number of digits is:

The number of characters is:

Enter string:Abc12

The number of digits is:

The number of characters is:

37.Program to Form a New String Made of the First 2 and Last 2 characters From a Given String

string=input("Enter string:")

count=0

for i in string:

count=count+1

new=string[0:2]+string[count-2:count]

print("Newly formed string is:")

print(new)

Output:

Enter string:Hello world

Newly formed string is:

Held

Enter string: manishbidsar

Newly formed string is:

Maar

38.Program to Count the Occurrences of Each Word in a Given String Sentence

string=input("Enter string:")

word=input("Enter word:")

a=[]

count=0

a=string.split(" ")

for i in range(0,len(a)):

if(word==a[i]):

count=count+1

print("Count of the word is:")

print(count)

Output:

Enter string: abc abc abc abc ddd bbb ccc

Enter word: abc

Count of the word is:

Enter string:orange blue red orange

Enter word:orange

Count of the word is:

39.Program to Check if a Substring is Present in a Given String

string=input("Enter string:")

sub_str=input("Enter word:")

if(string.find(sub_str)==-1):

print("Substring not found in string!")

else:

print("Substring found in string!")

Output:

Enter string:Hello world

Enter word:world

Substring in string!

Enter string:Hello world

Enter word:apple

Substring not found in string!

For Quick Recap on Strings watch the below videos:

Networking And Scripting

Sunday, 27 August 2017

Python String & String Programs

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