![Accessing Characters in String by Index Number
Each character in the string occupies a position in the string.
The first character is at index 0; the next character is at index 1, and so on.
The length of a string is the number of characters in it.
You can access each character in a string using a subscript operator i.e., a square bracket.
Square brackets are used to perform indexing in a string to get the value at a specific index or
position. This is also called subscript operator.
string_name[index]
index is usually in the range of 0 to len-1 or - from the end of the string starting from an
index number of −1(negative indexing)
1. >>> word_phrase = "be yourself”
2. >>> word_phrase[3] >>> word_phrase[-1]
‘y’ 'f'](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-9-320.jpg)
![String Slicing and Joining
A substring is created when slicing the strings . "slice" syntax : string_name[start:end[:step]]
1. >>> healthy_drink = "green tea"
2. >>> healthy_drink[0:3] >>> healthy_drink[-3:-1]
'gre‘ 'te'
3. >>> healthy_drink[:5] >>> healthy_drink[6:-1]
'green‘ 'te'
4. >>> healthy_drink[6:] >>> healthy_drink[::3]
'tea‘ ‘get’
5. >>> healthy_drink[:]
'green tea'
6. >>> healthy_drink[4:4]
‘’ empty string
7. >>> healthy_drink[6:20]
'tea'](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-11-320.jpg)
![String Slicing
Write Python Code to Determine Whether the Given String Is a Palindrome or Not Using Slicing
def main():
user_string = input("Enter string: ")
if user_string == user_string[::-1]:
print(f"User entered string is palindrome")
else:
print(f"User entered string is not a palindrome")
if __name__ == "__main__":
main()
Output
Case 1:
Enter string: madam
User entered string is palindrome](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-12-320.jpg)
![Joining Strings Using join() Method
1. >>> date_of_birth = ["17", "09", "1950"]
2. >>> ":".join(date_of_birth)
'17:09:1950'
3. >>> social_app = ["instagram", "is", "an", "photo", "sharing",
"application"]
4. >>> " ".join(social_app)
'instagram is an photo sharing application'
5. >>> numbers = "123"
6. >>> characters = "amy"
7. >>> password = numbers.join(characters)
8. >>> password
'a123m123y'](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-14-320.jpg)
![Split Strings Using split() Method
The split() method returns a list of string items by breaking up the string using the delimiter
string. The syntax of split() method is string_name.split([separator [, maxsplit]])
Separator - based on the specified separator, given string is split into list of strings,
Maxsplit - at most maxsplit splits are done, no limit – not specified or −1
1. >>> inventors = "edison, tesla, marconi, newton"
2. >>> inventors.split(",")
['edison', ' tesla', ' marconi', ' newton']
3. >>> watches = "rolex hublot cartier omega"
4. >>> watches.split()
['rolex', 'hublot', 'cartier', 'omega']](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-15-320.jpg)
![Strings Are Immutable
strings are immutable, it cannot be modified
can assign different string values to the same string variable.
1. >>> stre = "dollar"
2. >>> stre[0] = "c"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
3. >>> str1 = "c" + stre[1:]
4. >>> str1
'collar'
5. >>> stre = "rollar"
6. >>> stre
'rollar'](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-16-320.jpg)
![String Methods
1. >>> dir(str)
['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__',
'__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__',
'__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__
mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',
'__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize',
'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format',
'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit', 'isidentifier', 'islower',
'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip',
'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip',
'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
Various methods associated with str are displayed](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-18-320.jpg)
![F’string
f'string_statements {variable_name [: {width}.{precision}]}’
print(f'{name:10} ==> {phone:10d}') ...
>>> f'result: {value:{width}.{precision}}'](https://image.slidesharecdn.com/pythonprogramming-unit-ii-strings-250123041336-2d11aa9d/85/Python-Programming-UNIT-II-Strings-pptx-22-320.jpg)
Python Programming-UNIT-II - Strings.pptx
- 1. PYTHON PROGRAMMING UNIT II - STRINGS Dr. D.Kavitha
- 2. STRINGS A string consists of a sequence of characters, which includes letters, numbers, punctuation marks and spaces. To represent strings, you can use a single quote, double quotes or triple quotes. Creating and Storing Strings single_quote = 'This is a single message' 2. >>> double_quote = "Hey it is my book" 3. >>> single_char_string = "A" 4. >>> empty_string = "" 5. >>> empty_string = '' 6. >>> single_within_double_quote = "Opportunities don't happen. You create them.“ 8. >>> same_quotes = 'I've an idea' 9. >>> triple_quote_string = '''This … is … triple … quote'''
- 3. STRINGS A single character is also treated as string. A string does not need to have any characters in it - empty strings. A string enclosed in double quotation marks can contain single quotation marks if one type of quotation mark surrounds the string, you have to use the other type within it. If you want to include the same quotation marks within a string as you have used to enclose the string, then you need to preface the inner quote with a backslash. If you have a string spanning multiple lines, then it can be included within triple quotes. All white spaces and newlines used inside the triple quotes are literally reflected in the string You can find the type of a variable by passing it as an argument to type() function. Python strings are of str data type .
- 4. STRINGS The str() Function The str() function returns a string which is considered an informal or nicely printable representation of the given object. The syntax for str() function is, str(object) It returns a string version of the object. If the object is not provided, then it returns an empty string. 1. >>> str(10) '10' 2. >>> create_string = str() 3. >>> type(create_string) <class 'str'> Here integer type is converted to string type. Notice the single quotes to represent the string . The ➀ create_string is an empty string of type ➁ str . ➂
- 5. Basic String Operations + - operator is used to concatenate strings. Cannot use the + operator to concatenate values of two different types 1. >>> string_1 = "face" 2. >>> string_2 = "book" 3. >>> concatenated_string = string_1 + string_2 4. >>> concatenated_string 'facebook‘ singer = 50 + "cent" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'int' and 'str' 8. >>> singer = str(50) + "cent" 9. >>> singer '50cent'
- 6. Basic String Operations * - operator is used to create a repeated sequence of strings. >>> rep_of_string = "wow" * 5 >>> rep_of_string ‘wowwowwowwowwow’ presence of a string in another string using in and not in membership operators. 1. >>> fruit_string = "apple is a fruit" 2. >>> fruit_sub_string = "apple" 3. >>> fruit_sub_string in fruit_string True A substring is any sequence of characters that is contained in a string.
- 7. String Comparison Strings can be compared using various comparison operators (>, <, <=, >=, ==, !=) Python compares strings using ASCII value of the characters. 1. >>> "january" == "jane" False 2. >>> "january" != "jane" True 3. >>> "january" < "jane" False 4. >>> "january" > "jane" True 5. >>> "filled" > "" True
- 8. Built-In Functions Used on Strings Sample Built-In Functions and Description len() - The len() function calculates the number of characters in a string. The white space characters are also counted. max() - The max() function returns a character having highest ASCII value in given string. min() - The min() function returns character having lowest ASCII value. 1. >>> count_characters = len("eskimos") 2. >>> count_characters 7 3. >>> max("axel") 'x' 4. >>> min("brad") 'a'
- 9. Accessing Characters in String by Index Number Each character in the string occupies a position in the string. The first character is at index 0; the next character is at index 1, and so on. The length of a string is the number of characters in it. You can access each character in a string using a subscript operator i.e., a square bracket. Square brackets are used to perform indexing in a string to get the value at a specific index or position. This is also called subscript operator. string_name[index] index is usually in the range of 0 to len-1 or - from the end of the string starting from an index number of −1(negative indexing) 1. >>> word_phrase = "be yourself” 2. >>> word_phrase[3] >>> word_phrase[-1] ‘y’ 'f'
- 10. Accessing Characters in String by Index Number
- 11. String Slicing and Joining A substring is created when slicing the strings . "slice" syntax : string_name[start:end[:step]] 1. >>> healthy_drink = "green tea" 2. >>> healthy_drink[0:3] >>> healthy_drink[-3:-1] 'gre‘ 'te' 3. >>> healthy_drink[:5] >>> healthy_drink[6:-1] 'green‘ 'te' 4. >>> healthy_drink[6:] >>> healthy_drink[::3] 'tea‘ ‘get’ 5. >>> healthy_drink[:] 'green tea' 6. >>> healthy_drink[4:4] ‘’ empty string 7. >>> healthy_drink[6:20] 'tea'
- 12. String Slicing Write Python Code to Determine Whether the Given String Is a Palindrome or Not Using Slicing def main(): user_string = input("Enter string: ") if user_string == user_string[::-1]: print(f"User entered string is palindrome") else: print(f"User entered string is not a palindrome") if __name__ == "__main__": main() Output Case 1: Enter string: madam User entered string is palindrome
- 13. Joining Strings Using join() Method join() - concatenate strings. Syntax: string_name.join(sequence) sequence can be string or list. If the sequence is a string, then join() function inserts string_name between each character of the string sequence and returns the concatenated string. If the sequence is a list, then join() function inserts string_name between each item of list sequence and returns the concatenated string. It should be noted that all the items in the list should be of string type.
- 14. Joining Strings Using join() Method 1. >>> date_of_birth = ["17", "09", "1950"] 2. >>> ":".join(date_of_birth) '17:09:1950' 3. >>> social_app = ["instagram", "is", "an", "photo", "sharing", "application"] 4. >>> " ".join(social_app) 'instagram is an photo sharing application' 5. >>> numbers = "123" 6. >>> characters = "amy" 7. >>> password = numbers.join(characters) 8. >>> password 'a123m123y'
- 15. Split Strings Using split() Method The split() method returns a list of string items by breaking up the string using the delimiter string. The syntax of split() method is string_name.split([separator [, maxsplit]]) Separator - based on the specified separator, given string is split into list of strings, Maxsplit - at most maxsplit splits are done, no limit – not specified or −1 1. >>> inventors = "edison, tesla, marconi, newton" 2. >>> inventors.split(",") ['edison', ' tesla', ' marconi', ' newton'] 3. >>> watches = "rolex hublot cartier omega" 4. >>> watches.split() ['rolex', 'hublot', 'cartier', 'omega']
- 16. Strings Are Immutable strings are immutable, it cannot be modified can assign different string values to the same string variable. 1. >>> stre = "dollar" 2. >>> stre[0] = "c" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'str' object does not support item assignment 3. >>> str1 = "c" + stre[1:] 4. >>> str1 'collar' 5. >>> stre = "rollar" 6. >>> stre 'rollar'
- 17. String Traversing Characters of a string can be traversed using the for loop. Write Python Program to Calculate the Length of a String Without Using Built-In len() Function def main(): user_string = input("Enter a string: ") length = 0 for chr in user_string: length += 1 print(f"The length of user entered string is {length} ") if __name__ == "__main__": main()
- 18. String Methods 1. >>> dir(str) ['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill'] Various methods associated with str are displayed
- 19. Formatting Strings %-formatting str.format() f-strings - formatted strings %-formatting - int, str and doubles can be formatted. Pass only single value. %s - String (or any object with a string representation, like numbers) %d - Integers %f - Floating point numbers %.<number of digits>f - Floating point numbers with a fixed amount of digits to the right of the dot. %x/%X - Integers in hex representation (lowercase/uppercase) >>>import math >>> print('The value of pi is approximately %5.3f.' % math.pi) >>> The value of pi is approximately 3.142.
- 20. Str.format() The syntax for format() method is, str.format(p0, p1, ..., k0=v0, k1=v1, ...) where p0, p1,... are called as positional arguments and, k0, k1,... are keyword arguments with their assigned values of v0, v1,... respectively. Positional arguments are a list of arguments that can be accessed with an index of argument inside curly braces like {index}. Index value starts from zero. Keyword arguments are a list of arguments of type keyword = value, that can be accessed with the name of the argument inside curly braces like {keyword}. Here, str is a mixture of text and curly braces of indexed or keyword types
- 21. Str.format() 1. country = input("Which country do you live in?") 2. print("I live in {0}".format(country)) Output Which country do you live in? India I live in India 1. a = 10 2. b = 20 3. print("The values of a is {0} and b is {1}".format(a, b)) 4. print("The values of b is {1} and a is {0}".format(a, b)) Output The values of a is 10 and b is 20 The values of b is 20 and a is 10 1. >>> print("Give me {ball} ball".format(ball = "tennis")) Give me tennis ball
- 22. F’string f'string_statements {variable_name [: {width}.{precision}]}’ print(f'{name:10} ==> {phone:10d}') ... >>> f'result: {value:{width}.{precision}}'
- 23. Escape Sequences Escape Sequences are a combination of a backslash () followed by either a letter or a combination of letters and digits. Escape sequences are also called as control sequences. The backslash () character is used to escape the meaning of characters that follow it by substituting their special meaning with an alternate interpretation.
- 24. Raw Strings A raw string is created by prefixing the character r to the string. In Python, a raw string ignores all types of formatting within a string including the escape characters. 1. >>> print(r"Bible Says, "Taste and see that the LORD is good; blessed is the man who takes refuge in him."") Bible Says, "Taste and see that the LORD is good; blessed is the man who takes refuge in him. Unicodes Unicode Standard provides a unique number for every character, no matter what platform, device application or language. Ex: UTF-8, UTF-16, and UTF-32 Regular Python strings are not Unicode: they are just plain bytes. To create a Unicode string, use the 'u' prefix on the string literal. For example, 1. >>> unicode_string = u'A unicode u018e string xf1' 2. >>> unicode_string 'A unicode string ñ'