3.1 Strings revisited
3 min read•june 24, 2024
Strings Python are powerful tools for text manipulation. They can be sliced, indexed, and modified using various methods. Understanding how to work with strings is crucial for handling text data effectively in programming.
Special characters and escape sequences add flexibility to string representation. Unicode conversion functions allow working with a wide range of characters, while and formatting techniques enable complex text processing and presentation.
String Manipulation and Special Characters
String character indexing
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- Strings are sequences of characters that can be accessed and manipulated using
- Indexing starts at 0 for the first character and increments by 1 for each subsequent character (
accesses the first character)string[0] - Negative indexing starts at -1 for the last character and decrements by 1 for each preceding character (
accesses the last character)string[-1]
- Indexing starts at 0 for the first character and increments by 1 for each subsequent character (
- Individual characters can be accessed using square bracket notation
string[index] - Substrings can be extracted using slicing
string[start:end]
is the index of the first character to include (inclusive)start
is the index of the last character to exclude (exclusive)end- If
is omitted, it defaults to the beginning of the string (start
extracts the first 5 characters)string[:5] - If
is omitted, it defaults to the end of the string (end
extracts from the 3rd character to the end)string[2:]
- Strings are immutable, meaning individual characters cannot be directly modified
- To modify a string, create a new string with the desired changes (concatenate, slice, etc.)
Escape sequences in strings
- Escape sequences are used to represent special characters within a string ()
- Escape sequences start with a backslash
followed by a specific character or\ - Common escape sequences include:
inserts a newline[\n](https://www.fiveableKeyTerm:\n)
inserts a tab[\t](https://www.fiveableKeyTerm:\t)
inserts a literal backslash\\
inserts a single quote\'
inserts a double quote\"
- Escape sequences are treated as a single character within the string
- Raw strings (prefixed with
orr
) treat backslashes as literal characters, ignoring escape sequences (R
preserves the backslashes)r"C:\newfile"
Unicode conversion functions
- Unicode is a standard for representing a wide range of characters from various scripts and symbols
- Each character is assigned a unique code point, which is an integer value
- The
function takes a single character as an argument and returns its Unicode code point[ord()](https://www.fiveableKeyTerm:ord())
returnsord('A')65
returnsord('€')8364
- The
function takes a Unicode code point as an argument and returns the corresponding character[chr()](https://www.fiveableKeyTerm:chr())
returnschr(65)'A'
returnschr(8364)'€'
- These functions allow for conversion between characters and their numerical representations
- Unicode code points can be used for character comparisons and manipulations
evaluates toord('A') < ord('B')True
returnschr(ord('A') + 1)'B'
String Operations and Formatting
- String operations allow for manipulation and combination of strings
- : Joining strings using the
operator+ - Repetition: Repeating strings using the
operator*
- : Joining strings using the
- uses relational operators to compare strings lexicographically
,<
,>
,<=
,>=
,==
can be used to compare strings!=
- provide built-in functionality for string manipulation
- Common methods include
,lower()
,upper()
,strip()
,split()join()
- Common methods include
- String formatting allows for creating formatted strings with placeholders
- :
for inline variable substitutionf"Hello, {name}!"
method:.format()
for more complex formatting"Hello, {}!".format(name)
- :
Key Terms to Review (25)
\n: The newline character, denoted as '\n', is a special character in programming that represents the end of a line of text and the start of a new line. It is a fundamental concept in input/output operations, string basics, and string manipulation in Python.
\t: \t is a special character in programming languages, including Python, that represents a horizontal tab. It is used to insert a tab space, which can be useful for aligning text or creating formatted output.
Chr(): The chr() function in Python is used to return a string representing a character whose Unicode code point is the integer passed as an argument. It is a fundamental string operation that allows you to manipulate and work with individual characters within a string.
Concatenation: Concatenation is the operation of joining two or more strings end-to-end to create a single string. This process is a fundamental aspect of working with text in programming, as it allows for dynamic string creation, manipulation, and formatting. Understanding concatenation is essential for tasks involving user input, data display, and creating readable outputs in code.
Escape Characters: Escape characters are special characters used in programming to represent certain actions or non-printable characters. They are denoted by a backslash (\) followed by a specific character and are used to create special formatting or control the behavior of a string.
Escape sequence: An escape sequence is a series of characters used to represent special characters in a string. It typically begins with a backslash followed by one or more characters.
F-strings: F-strings, also known as formatted string literals, are a powerful feature in Python that allow for easy and efficient string formatting. They provide a concise way to embed expressions directly within string literals, making it simpler to create dynamic and customizable strings.
Immutability: Immutability refers to the property of an object or a variable where its value cannot be changed or modified once it has been created. This concept is fundamental in programming and has important implications in various contexts, including string operations, tuple handling, and dictionary management.
In: The term 'in' is a preposition that is used to indicate location, time, or inclusion within a specific context. It is a fundamental part of the English language and plays a crucial role in various programming concepts, including string manipulation, list operations, dictionary usage, and control flow structures.
Indexing: Indexing is the process of accessing specific elements within a data structure, such as a string, list, or array, by their position or index. It allows for the retrieval, manipulation, and identification of individual components within a larger collection of data.
Interpolation: Interpolation is the process of estimating or approximating a value within a range of known data points. It involves using existing information to estimate unknown values, often in the context of data analysis, numerical methods, and programming languages like Python.
Iterable: An iterable is an object that can be iterated over, meaning it can be used in a loop or other sequence-based operations. Iterables are fundamental to many programming concepts, including strings, tuples, lists, and more.
Keyword arguments: Keyword arguments in Python are function arguments where the parameter name is explicitly mentioned. This allows for more readable code and provides flexibility in the order of arguments.
Len(): The len() function is a built-in function in Python that returns the length or count of elements in a given object, such as a string, list, tuple, or dictionary. It is a fundamental operation that is widely used across various programming topics in Python.
Ord(): The ord() function in Python returns the Unicode code point of a given character. It is a built-in function that provides a way to obtain the numeric representation of a character, which can be useful in various string manipulation and processing tasks.
Sequence: A sequence is an ordered arrangement of elements, such as numbers, letters, or objects, that follow a specific pattern or order. This concept is fundamental in various areas of computer science and mathematics, including programming, data structures, and algorithms.
Str: The str (string) data type in Python is a collection of one or more characters that can include letters, digits, and various symbols. Strings are used to represent and manipulate textual data within a Python program.
Str.format(): The str.format() method is a powerful tool in Python that allows you to insert values into a string in a more flexible and readable way than traditional string concatenation. It provides a way to format strings by replacing placeholders with specified values, making it a versatile and efficient approach for creating dynamic and customized output.
Str.split(): The str.split() method is a built-in function in Python that takes a string and divides it into a list of substrings based on a specified delimiter. This operation is particularly useful for extracting data from structured text formats, such as CSV files or API responses, where information is separated by a consistent character or pattern.
Str.strip(): The str.strip() method is a built-in Python function that removes any leading or trailing whitespace characters, such as spaces, tabs, and newlines, from a given string. This is a useful tool for cleaning up and formatting string data in Python.
String Comparison: String comparison refers to the process of evaluating and comparing the values of two or more strings to determine their relationship, such as whether they are equal, one is greater than the other, or they are lexicographically ordered. This concept is fundamental in programming and is utilized across various topics related to string manipulation and processing.
String Methods: String methods are built-in functions in Python that allow you to perform various operations and manipulations on string data types. These methods provide a wide range of functionalities, from modifying the case of characters to searching, splitting, and joining strings, making it easier to work with and process textual information.
String Operations: String operations refer to the various actions and manipulations that can be performed on text-based data, known as strings, in programming languages like Python. These operations allow developers to create, modify, and analyze textual information to meet the requirements of their applications.
String slicing: String slicing is the process of extracting a portion of a string by specifying a start and end index. It allows for accessing substrings in Python efficiently.
String Slicing: String slicing is a fundamental operation in Python that allows you to extract a substring from a larger string. It involves selecting a specific portion of a string based on its position within the string.