Strings — Python (Part 2)
The chr() and ord() methods in Python are used to convert between characters and their corresponding ASCII or Unicode values. Here’s a detailed explanation and some examples to illustrate how they work.
chr()
The chr() function returns the string representing a character whose Unicode code point is the integer passed as an argument. For ASCII values, this ranges from 0 to 127.
Syntax:
chr(i)
i: An integer representing a Unicode code point.
Examples:
print(chr(65)) # Output: 'A'
print(chr(97)) # Output: 'a'
print(chr(8364)) # Output: '€' (Euro sign)
ord()
The ord() function returns an integer representing the Unicode code point of the given Unicode character.
Syntax:
ord(c)
c: A single Unicode character.
Examples:
print(ord('A')) # Output: 65
print(ord('a')) # Output: 97
print(ord('€')) # Output: 8364
Combining chr() and ord()
You can use chr() and ord() together to encode and decode characters.
Example:
char = 'G'
encoded = ord(char)
decoded = chr(encoded)
print(f"Character: {char}, Encoded: {encoded}, Decoded: {decoded}")
# Output: Character: G, Encoded: 71, Decoded: G
Practical Examples
Printing Characters in a Sequence
You can use a loop to print a sequence of characters.
Example:
# Print uppercase A to Z
for i in range(65, 91):
print(chr(i), end=' ')
# Output: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Creating a String of Incremental Characters
You can create a string by accumulating characters in a loop.
Example:
str1 = ""
for i in range(4):
str1 += chr(65 + i)
print(str1)
# Output:
# A
# AB
# ABC
# ABCD
Reversing a String
You can reverse the process by printing progressively shorter substrings.
Example:
str1 = "ABCD"
for i in range(len(str1)):
print(str1[:len(str1) - i])
# Output:
# ABCD
# ABC
# AB
# A
Unicode Characters
Both chr() and ord() work with Unicode, which allows for a vast range of characters beyond ASCII.
Example:
print(chr(128512)) # Output: '😀' (Grinning Face emoji)
print(ord('😀')) # Output: 128512
Application in Data Processing
The chr() and ord() functions can be useful in various scenarios, such as:
Generating sequences of characters programmatically.
Encoding and decoding messages.
Working with character data in encryption and compression algorithms.
String Methods Overview
Case Conversion Methods
str.upper()str.lower()str.capitalize()str.title()str.swapcase()
Whitespace Removal Methods
str.strip()str.lstrip()str.rstrip()
Search and Check Methods
str.startswith()str.endswith()str.find()str.index()str.rfind()str.rindex()
Content Test Methods
str.isupper()str.islower()str.isalpha()str.isdigit()str.isalnum()str.isspace()str.istitle()str.isidentifier()str.isprintable()
String Modification Methods
str.replace()str.split()str.join()str.partition()str.ljust()str.rjust()str.zfill()
Additional Methods
str.casefold()str.splitlines()
Detailed Examples
1. Case Conversion Methods
str.upper(): Converts all characters to uppercase.
print("hello".upper()) # Output: 'HELLO'
str.lower(): Converts all characters to lowercase.
print("HELLO".lower()) # Output: 'hello'
str.capitalize(): Capitalizes the first character and lowercases the rest.
print("hello world".capitalize()) # Output: 'Hello world'
str.title(): Capitalizes the first character of each word.
print("hello world".title()) # Output: 'Hello World'
str.swapcase(): Swaps the case of each character.
print("Hello World".swapcase()) # Output: 'hELLO wORLD'
2. Whitespace Removal Methods
str.strip(): Removes leading and trailing whitespace.
print(" hello ".strip()) # Output: 'hello'
str.lstrip(): Removes leading whitespace.
print(" hello ".lstrip()) # Output: 'hello '
str.rstrip(): Removes trailing whitespace.
print(" hello ".rstrip()) # Output: ' hello'
3. Search and Check Methods
str.startswith(): Checks if the string starts with the specified substring.
print("hello world".startswith("hello")) # Output: True
str.endswith(): Checks if the string ends with the specified substring.
print("hello world".endswith("world")) # Output: True
str.find(): Returns the lowest index of the substring if found, otherwise -1.
print("hello world".find("world")) # Output: 6
str.index(): Returns the lowest index of the substring if found, otherwise raises a ValueError.
print("hello world".index("world")) # Output: 6
str.rfind(): Returns the highest index of the substring if found, otherwise -1.
print("hello world hello".rfind("hello")) # Output: 12
str.rindex(): Returns the highest index of the substring if found, otherwise raises a ValueError.
print("hello world hello".rindex("hello")) # Output: 12
4. Content Test Methods
str.isupper(): Checks if all characters are uppercase.
print("HELLO".isupper()) # Output: True
str.islower(): Checks if all characters are lowercase.
print("hello".islower()) # Output: True
str.isalpha(): Checks if all characters are alphabetic.
print("hello".islower()) # Output: True
str.isdigit(): Checks if all characters are digits.
print("12345".isdigit()) # Output: True
str.isalnum(): Checks if all characters are alphanumeric.
print("hello123".isalnum()) # Output: True
str.isspace(): Checks if all characters are whitespace.
print(" ".isspace()) # Output: True
str.istitle(): Checks if each word is capitalized.
print("Hello World".istitle()) # Output: True
str.isidentifier(): Checks if the string is a valid identifier.
print("variable_name".isidentifier()) # Output: True
str.isprintable(): Checks if all characters are printable.
print("Hello World!".isprintable()) # Output: True
5. String Modification Methods
str.replace(): Replaces occurrences of a substring with another substring.
print("hello world".replace("world", "Python")) # Output: 'hello Python'
str.split(): Splits the string into a list of substrings.
print("hello world".split()) # Output: ['hello', 'world']
str.join(): Joins elements of an iterable with the string as a separator.
print(", ".join(["apple", "banana", "cherry"])) # Output: 'apple, banana, cherry'
str.partition(): Splits the string at the first occurrence of the separator into a tuple.
print("hello world".partition(" ")) # Output: ('hello', ' ', 'world')
str.center(): Centers the string with specified width and fill character.
print("hello".center(10, '-')) # Output: '--hello---'
str.ljust(): Left-justifies the string with specified width and fill character.
print("hello".ljust(10, '-')) # Output: 'hello-----'
str.rjust(): Right-justifies the string with specified width and fill character.
print("hello".rjust(10, '-')) # Output: '-----hello'
str.zfill(): Pads the string on the left with zeros to fill the specified width.
print("42".zfill(5)) # Output: '00042'
6. Additional Methods
str.casefold(): Converts the string to lowercase in a way that is aggressive and suitable for caseless comparisons.
print("Groß".casefold()) # Output: 'gross'
str.splitlines(): Splits the string at line breaks and returns a list of lines.
print("first line\nsecond line\nthird line".splitlines()) # Output: ['first line'
