Strings — Python (Part 2)

Strings — Python (Part 2)

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Akshima Sharma
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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.center()

  • 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'
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