A string is an immutable sequence of characters used to represent text in Python. Strings are enclosed in single quotes ‘…’, double quotes “…”, or triple quotes ”’…”’\/”””…””” for multi-line strings.<\/p>\n
greeting = “Hello, world!”<\/em><\/p>\n Common String Methods<\/strong><\/p>\n String methods are built-in functions you can use to manipulate or inspect strings. They do not change the original string but return a new one.<\/p>\n lower() \/ upper()<\/strong><\/p>\n Converts all characters to lowercase or uppercase.<\/p>\n “Python”.lower() # ‘python’<\/em> capitalize() \/ title()<\/strong><\/p>\n Capitalizes the first character or the first letter of each word.<\/p>\n “hello world”.capitalize() # ‘Hello world’<\/em> strip(), lstrip(), rstrip()<\/strong><\/p>\n Removes whitespace or specified characters from both\/single sides.<\/p>\n ” hello “.strip() # ‘hello’<\/em> replace(old, new)<\/strong><\/p>\n Replaces part of the string with something else.<\/p>\n “cats are cool”.replace(“cats”, “dogs”) # ‘dogs are cool’<\/em><\/p>\n split(separator) \/ join(iterable)<\/strong><\/p>\n “one,two,three”.split(‘,’) # [‘one’, ‘two’, ‘three’]<\/em> find() \/ index()<\/strong><\/p>\n Returns the position of the first occurrence of a substring. find() returns -1 if not found, while index() raises an error.<\/p>\n “hello”.find(“e”) # 1<\/em> startswith() \/ endswith()<\/strong><\/p>\n Checks if a string starts or ends with a given substring.<\/p>\n “url.com”.startswith(“http”) # False<\/em> count(substring)<\/strong><\/p>\n Counts how many times a substring occurs.<\/p>\n “banana”.count(“a”) # 3<\/em><\/p>\n isalpha(), isdigit(), isalnum(), isspace()<\/strong><\/p>\n Check string properties:<\/p>\n “abc”.isalpha() # True<\/em> Python offers multiple ways to insert variables into strings.<\/p>\n 1. f-Strings (Python 3.6+) \u2013 Best and cleanest<\/strong><\/p>\n name = “Alice”<\/em> 2. .format() Method<\/strong><\/p>\n “Hello, {}. You are {}.”.format(“Bob”, 25)<\/em><\/p>\n With named placeholders:<\/p>\n “Hello, {name}. You are {age}.”.format(name=”Bob”, age=25)<\/em><\/p>\n 3. Percent (%) Formatting \u2013 Older style<\/strong><\/p>\n “%s is %d years old.” % (“Tom”, 40)<\/em><\/p>\n Advanced f-String Features<\/strong><\/p>\n You can even evaluate expressions inside f-strings:<\/p>\n price = 19.99<\/em> Summary:<\/strong><\/p>\n f-strings are a string formatting method introduced in Python 3.6 that allow you to embed expressions directly inside string literals using {} brackets, prefixed by an f or F.<\/p>\n name = “Alice”<\/em> Syntax<\/strong><\/p>\n f”some text {expression} more text”<\/em><\/p>\n Basic Examples<\/strong><\/p>\n name = “Bob”<\/em> Expressions Inside f-Strings<\/strong><\/p>\n You can evaluate any valid expression inside {}:<\/p>\n a = 5<\/em> You can also call functions:<\/p>\n def greet(name):<\/em> print(f”{greet(‘Alice’)}, welcome!”)<\/em> Formatting Numbers<\/strong><\/p>\n Decimal Precision:<\/strong><\/p>\n pi = 3.14159<\/em> Thousand Separators:<\/strong><\/p>\n big_number = 1000000<\/em> Formatting Dates<\/strong><\/p>\n You can format datetime objects too:<\/p>\n from datetime import datetime<\/em> Debugging with f-Strings (Python 3.8+)<\/strong><\/p>\n Using the = sign shows both the variable and its value:<\/p>\n f-Strings vs Other Methods<\/strong><\/p>\n What f-Strings Can’t Do<\/strong><\/p>\n Summary:<\/strong><\/p>\n String slicing means extracting a portion (substring) of a string using its index positions. It\u2019s done using colon (:) notation within square brackets.<\/p>\n text = “Python”<\/em> Syntax<\/strong><\/p>\n string[start:stop:step]<\/em><\/p>\n Indexing Recap<\/strong><\/p>\n Python strings are zero-indexed:<\/strong><\/p>\n Index: 0 1 2 3 4 5<\/em> Basic Examples<\/strong><\/p>\n text = “Python”<\/em><\/p>\n print(text[0:4]) # ‘Pyth’ (characters 0 to 3)<\/em> Using Negative Indices<\/strong><\/p>\n print(text[-3:]) # ‘hon’<\/em> Slicing with Steps<\/strong><\/p>\n print(text[::2]) # ‘Pto’ (every second character)<\/em> Real-World Examples<\/strong><\/p>\n Extract domain from email:<\/strong><\/p>\n email = “user@example.com”<\/em> Capitalize only the first letter manually:<\/strong><\/p>\n word = “python”<\/em> Out-of-Range Slicing<\/strong><\/p>\n Slicing gracefully handles out-of-bounds indices:<\/strong><\/p>\n text = “abc”<\/em> Summary:<\/strong><\/p>\n Escape characters let you insert characters into strings that are otherwise hard to type or have special meaning \u2014 like quotes, tabs, newlines, etc.<\/p>\n They all begin with a backslash (\\).<\/p>\n Common Escape Characters:<\/strong><\/p>\n Example:<\/strong> Escape in Action<\/p>\n quote = “She said, \\”Hello there!\\””<\/em> path = “C:\\\\Users\\\\Name\\\\Desktop”<\/em> Raw strings treat backslashes (\\) literally. Nothing is escaped.<\/p>\n They are prefixed with r or R.<\/p>\n raw_path = r”C:\\Users\\New\\Notes”<\/em> No need to double up the \\\\ when using raw strings!<\/p>\n When to Use Raw Strings<\/strong><\/p>\n import re<\/em> Important Note<\/strong><\/p>\n Even raw strings can\u2019t end with a single backslash \u2014 it escapes the quote:<\/p>\n r”test\\\\” Valid<\/em> Summary:<\/strong><\/p>\n
\n“code”.upper() # ‘CODE’<\/em><\/p>\n
\n“python is fun”.title() # ‘Python Is Fun’<\/em><\/p>\n
\n“—text—“.strip(‘-‘) # ‘text’<\/em><\/p>\n\n
\n“,”.join([“a”, “b”, “c”]) # ‘a,b,c’<\/em><\/p>\n
\n“hello”.index(“e”) # 1<\/em><\/p>\n
\n“url.com”.endswith(“.com”) # True<\/em><\/p>\n
\n“123”.isdigit() # True<\/em>
\n“abc123”.isalnum() # True<\/em>
\n” “.isspace() # True<\/em><\/p>\nString Formatting in Python<\/h3>\n
\nage = 30<\/em>
\nprint(f”My name is {name} and I’m {age} years old.”)<\/em><\/p>\n
\nprint(f”Total after tax: ${price * 1.07:.2f}”) # Format to 2 decimal places<\/em><\/p>\n\n
f-strings<\/h2>\n
What Are f-Strings?<\/h3>\n
\nprint(f”Hello, {name}!”) # Output: Hello, Alice!<\/em><\/p>\n\n
\nage = 30<\/em>
\nprint(f”{name} is {age} years old.”)<\/em>
\n# Output: Bob is 30 years old.<\/em><\/p>\n
\nb = 3<\/em>
\nprint(f”{a} + {b} = {a + b}”)<\/em>
\n# Output: 5 + 3 = 8<\/em><\/p>\n
\nreturn f”Hello, {name}!”<\/em><\/p>\n
\n# Output: Hello, Alice!, welcome!<\/em><\/p>\n
\nprint(f”Value of pi: {pi:.2f}”) # Output: Value of pi: 3.14<\/em><\/p>\n
\nprint(f”{big_number:,}”) # Output: 1,000,000<\/em><\/p>\n
\nnow = datetime.now()<\/em>
\nprint(f”Date: {now:%Y-%m-%d}, Time: {now:%H:%M}”)<\/em><\/p>\n\n\n
\n Method<\/strong><\/th>\n Readability<\/strong><\/th>\n Performance<\/strong><\/th>\n Flexibility<\/strong><\/th>\n<\/tr>\n<\/thead>\n\n \n f-string<\/td>\n Best<\/td>\n Fastest<\/td>\n High<\/td>\n<\/tr>\n \n .format()<\/td>\n Okay<\/td>\n Slower<\/td>\n High<\/td>\n<\/tr>\n \n %<\/td>\n Outdated<\/td>\n Slower<\/td>\n Low<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
\n
String slicing<\/h2>\n
What Is String Slicing?<\/h3>\n
\nprint(text[0:2]) # Output: Py<\/em><\/p>\n\n
\nString: P y t h o n<\/em>
\n-6 -5 -4 -3 -2 -1 (negative indexing)<\/em><\/p>\n
\nprint(text[:3]) # ‘Pyt’ (start defaults to 0)<\/em>
\nprint(text[2:]) # ‘thon’ (to the end)<\/em>
\nprint(text[:]) # ‘Python’ (whole string)<\/em><\/p>\n
\nprint(text[:-2]) # ‘Pytho’ (up to index -2, exclusive)<\/em><\/p>\n
\nprint(text[::-1]) # ‘nohtyP’ (reversed string)<\/em><\/p>\n
\ndomain = email[email.index(“@”)+1:]<\/em>
\nprint(domain) # ‘example.com’<\/em><\/p>\n
\nresult = word[0].upper() + word[1:]<\/em>
\nprint(result) # ‘Python’<\/em><\/p>\n
\nprint(text[0:100]) # ‘abc’ (no error)<\/em><\/p>\n\n
Escape characters and raw strings<\/h2>\n
What Are Escape Characters?<\/h3>\n
\n\n
\n Escape<\/strong><\/th>\n Meaning<\/strong><\/th>\n Example<\/strong><\/th>\n<\/tr>\n<\/thead>\n\n \n \\’<\/td>\n Single quote<\/td>\n ‘It\\’s Python’ \u2192 It’s Python<\/td>\n<\/tr>\n \n \\”<\/td>\n Double quote<\/td>\n “He said, \\”Hi\\”” \u2192 He said, “Hi”<\/td>\n<\/tr>\n \n \\\\<\/td>\n Backslash<\/td>\n ‘C:\\\\path\\\\file’ \u2192 C:\\path\\file<\/td>\n<\/tr>\n \n \\n<\/td>\n Newline<\/td>\n ‘Line1\\nLine2’<\/td>\n<\/tr>\n \n \\t<\/td>\n Tab<\/td>\n ‘A\\tB’ \u2192 A\u2003B<\/td>\n<\/tr>\n \n \\r<\/td>\n Carriage return<\/td>\n ‘123\\rABC’ \u2192 ABC<\/td>\n<\/tr>\n \n \\b<\/td>\n Backspace<\/td>\n ‘A\\bB’ \u2192 B<\/td>\n<\/tr>\n \n \\a<\/td>\n Bell (system sound)<\/td>\n May trigger a beep<\/td>\n<\/tr>\n \n \\f<\/td>\n Form feed<\/td>\n Page break in printing<\/td>\n<\/tr>\n \n \\v<\/td>\n Vertical tab<\/td>\n Rarely used<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\nprint(quote)<\/em>
\n# Output: She said, “Hello there!”<\/em><\/p>\n
\nprint(path)<\/em>
\n# Output: C:\\Users\\Name\\Desktop<\/em><\/p>\nWhat Are Raw Strings?<\/h3>\n
\nprint(raw_path)<\/em>
\n# Output: C:\\Users\\New\\Notes<\/em><\/p>\n\n
\npattern = r”\\d{3}-\\d{2}-\\d{4}” # Raw string for regex<\/em><\/p>\n
\nr”test\\” SyntaxError<\/em><\/p>\n\n