Python chr(): Converting Unicode Code Points to String Characters

1. Syntax & Parameter Specifications 🔝

The chr() function takes a single integer argument representing a Unicode code point:

# Formal syntax of built-in chr()
character = chr(i)

Unicode Code Point Ranges Overview

2. Converting ASCII Integers to Printable Characters 🔝

The first 128 integers (0 to 127) directly mirror the universal ASCII character mapping:

# 1. Converting ASCII integers to printable characters
print("Code point 65: ", chr(65))    # 'A'
print("Code point 97: ", chr(97))    # 'a'
print("Code point 48: ", chr(48))    # '0'
print("Code point 64: ", chr(64))    # '@'
print("Code point 38: ", chr(38))    # '&'

Terminal Output:

Code point 65:  A
Code point 97:  a
Code point 48:  0
Code point 64:  @
Code point 38:  &

3. Accessing Extended Unicode & Emoji Characters 🔝

Beyond standard ASCII, chr() accesses international alphabets, currency signs, and modern emojis:

# 2. Accessing Unicode planes: Latin-1, Currency, and Emojis
# Latin-1 Supplement (128 - 255)
print("chr(233) [accented e]:  ", chr(233))     # 'é'
print("chr(241) [enye]:        ", chr(241))     # 'ñ'

# Currency symbols (BMP: 256 - 65535)
print("chr(8364) [Euro]:       ", chr(8364))    # '€'
print("chr(163)  [Pound]:      ", chr(163))     # '£'

# Supplementary Plane emojis (65536 - 1114111)
print("chr(128640) [Rocket]:   ", chr(128640))  # '🚀'
print("chr(128512) [Grinning]: ", chr(128512))  # '😀'

Terminal Output:

chr(233) [accented e]:   é
chr(241) [enye]:         ñ
chr(8364) [Euro]:        €
chr(163)  [Pound]:       £
chr(128640) [Rocket]:    🚀
chr(128512) [Grinning]:  😀

4. Bidirectional Symmetry: chr() vs. ord() 🔝

chr() and ord() are exact mathematical inverses of one another:

• chr(ord(c)) == c for any single character string c.
• ord(chr(i)) == i for any integer code point i in range 0 through 1,114,111.

# 3. Mathematical symmetry: chr() and ord() as inverse functions
original_char = 'Ω'  # Greek capital Omega
code_point = ord(original_char)
recovered_char = chr(code_point)

print("Original character: ", original_char)
print("ord() code point:   ", code_point)
print("chr() restored char:", recovered_char)
print("Symmetry holds:     ", original_char == recovered_char)

Terminal Output:

Original character:  Ω
ord() code point:    937
chr() restored char: Ω
Symmetry holds:      True

5. Generating Alphabet Sequences with List Comprehensions 🔝

Using chr() inside list comprehensions over range() creates clean alphabet sequences without hardcoding character lists:

# 4. Generating alphabet sequences using list comprehensions
uppercase_letters = [chr(i) for i in range(65, 91)]
lowercase_letters = [chr(i) for i in range(97, 123)]
digits_chars = [chr(i) for i in range(48, 58)]

print("Uppercase (A-Z):", "".join(uppercase_letters))
print("Lowercase (a-z):", "".join(lowercase_letters))
print("Digits (0-9):   ", "".join(digits_chars))

Terminal Output:

Uppercase (A-Z): ABCDEFGHIJKLMNOPQRSTUVWXYZ
Lowercase (a-z): abcdefghijklmnopqrstuvwxyz
Digits (0-9):    0123456789

6. Production Recipes 🔝

Combining chr() and ord() enables classic algorithmic transformations like the Caesar cipher and dynamic character set generation:

# 5. Production Recipe: Reversible Caesar Cipher
def caesar_cipher(text: str, shift: int = 3) -> str:
    """Encrypts or decrypts text using modular arithmetic with chr() and ord()."""
    result = []
    for ch in text:
        if ch.isalpha():
            base = ord('A') if ch.isupper() else ord('a')
            shifted = chr((ord(ch) - base + shift) % 26 + base)
            result.append(shifted)
        else:
            result.append(ch)
    return "".join(result)

secret_msg = "Python Programming on plus2net!"
encrypted = caesar_cipher(secret_msg, shift=5)
decrypted = caesar_cipher(encrypted, shift=-5)

print("Original: ", secret_msg)
print("Encrypted:", encrypted)
print("Decrypted:", decrypted)

Terminal Output:

Original:  Python Programming on plus2net!
Encrypted: Udymts Uwtlwfrrnsl ts uqzx2sjy!
Decrypted: Python Programming on plus2net!

Generating custom alphanumeric and symbolic character ranges:

# 6. Production Recipe: Deterministic Character Range Generator
def generate_charset(ranges):
    """Generates a custom character sequence from start/stop integer tuples."""
    chars = []
    for start, stop in ranges:
        chars.extend(chr(i) for i in range(start, stop + 1))
    return "".join(chars)

# Generate alphanumeric and math symbol set
custom_charset = generate_charset([(65, 70), (97, 102), (945, 950)])
print("Custom generated charset:", custom_charset)

Terminal Output:

Custom generated charset: ABCDEFabcdefαβγδεζ

7. Common Developer Pitfalls & Traps 🔝

Ensure that values passed to chr() are strictly integers within the allowed Unicode range:

# 7. Common traps: TypeError (floats/strings) & ValueError (range bounds)
# Trap 1: Passing float values raises TypeError
try:
    chr(65.0)
except TypeError as err:
    print("TypeError caught:", err)

# Trap 2: Out of bounds code point (> 1114111) raises ValueError
try:
    chr(1114112)
except ValueError as err:
    print("ValueError caught:", err)

Terminal Output:

TypeError caught: an integer is required (got type float)
ValueError caught: chr() arg not in range(0x110000)

8. Interactive Notebook & Practice Exercises 🔝

Explore character code point transformations, Unicode planes, and cipher algorithms in our interactive companion Jupyter Notebook:

Self-Verifying Assertion Suite

Run these unit checks directly in Python or your local environment to verify chr() mechanics:

# 8. Self-verifying unit test suite for chr()
# Test 1: ASCII character lookup
assert chr(65) == 'A' and chr(90) == 'Z'
assert chr(97) == 'a' and chr(122) == 'z'

# Test 2: Extended Unicode & Emojis
assert chr(233) == 'é'
assert chr(8364) == '€'
assert chr(128640) == '🚀'

# Test 3: Symmetry with ord()
for code in [32, 65, 126, 233, 1000, 128512]:
    assert ord(chr(code)) == code

# Test 4: Range boundary checks
assert chr(0) == '\x00'
assert chr(1114111) == '\U0010ffff'

print("All chr() unit assertions successfully verified!")

Terminal Output:

All chr() unit assertions successfully verified!

9. Frequently Asked Questions (FAQ) 🔝

Further Reading & Related Tutorials 🔝

• Python ord() Function — Converting characters to their integer Unicode code point values.
• Python ascii() Function — Converting non-ASCII characters to printable escape sequences.
• Python str() Function — String data handling, formatting, and unicode representations.
• Python bytes() Function — Creating and manipulating immutable byte sequences.
• Python range() Function — Generating integer progressions for character iteration.
• All Built-in Functions — Complete index of standard Python built-ins.

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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