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ascii() Function Complexity

The ascii() function returns a printable representation of an object with non-ASCII characters escaped.

Complexity Analysis

Case Time Space Notes
ASCII string O(n) O(n) n = string length
Unicode string O(n) O(n) Non-ASCII chars escaped
Container O(n) O(n) Recursively escapes contents
Custom object O(1)* O(1)* Depends on __repr__

Basic Usage

ASCII Strings

# O(n) - where n = string length
ascii("hello")       # "'hello'"
ascii("Python")      # "'Python'"
ascii("123")         # "'123'"

Unicode Strings

# O(n) - non-ASCII characters escaped
ascii("café")        # "'caf\\xe9'"
ascii("🎵")         # "'\\U0001f3b5'"
ascii("Ñoño")        # "'\\xd1o\\xf1o'"
ascii("日本語")       # "'\\u65e5\\u672c\\u8a9e'"

Mixed Content

# O(n) - escapes all non-ASCII
text = "Hello, 世界"
ascii(text)  # "'Hello, \\u4e16\\u754c'"

# Each Unicode character escaped to \uXXXX or \UXXXXXXXX

Complexity Details

Character Escaping

# O(n) - linear in string length
# Each character may expand to multiple chars

# Short ASCII
ascii("abc")  # O(3)

# Long ASCII
ascii("a" * 1000)  # O(1000)

# Unicode requiring escaping
ascii("é" * 100)   # O(100) - each é becomes \xé9 (5 chars)

Escape Sequences

# ASCII characters - no change
# Extended ASCII (127-255) - use \xHH format (4 chars total)
ascii("\xe9")  # "'\\xe9'" - é in Latin-1

# Unicode (>255) - use \uHHHH format (6 chars total)
ascii("\u0101")  # "'\\u0101'" - ā (a with macron)

# High Unicode - use \UHHHHHHHH format (10 chars total)
ascii("\U0001f600")  # "'\\U0001f600'" - 😀 emoji

Common Patterns

Debugging Non-ASCII Content

# O(n) - show hidden non-ASCII characters
text = "Hello\nWorld\t!"
print(ascii(text))
# Output: 'Hello\\nWorld\\t!'

# vs str/repr
print(str(text))    # Shows actual newlines/tabs
print(repr(text))   # Shows escapes but uses non-ASCII if present

# ascii() always shows escapes
text_unicode = "Héllo"
print(repr(text_unicode))   # "'Héllo'" (shows Unicode char)
print(ascii(text_unicode))  # "'H\\xe9llo'" (escaped)

Encoding for Limited Charsets

# O(n) - ensure output is 7-bit ASCII safe
def make_ascii_safe(text):
    return ascii(text)

data = "Café: 100€"
safe = make_ascii_safe(data)
# "'Caf\\xe9: 100\\u20ac'"

# Can send safely over ASCII-only channels

File Names and Paths

# O(n) - display paths with non-ASCII names
import os

# Filename might contain Unicode
filename = "documento_españa.txt"
print(ascii(filename))
# "'documento_espa\\xf1a.txt'"

# Safe for logging
path = "/home/用户/文件.txt"
print(ascii(path))
# "'/home/\\u7528\\u6237/\\u6587\\u4ef6.txt'"

Comparison with Alternatives

ascii() vs repr()

# Both O(n), but different escaping

text = "Café"

# repr() - shows non-ASCII directly (Python 3)
repr(text)   # "'Café'"

# ascii() - escapes all non-ASCII
ascii(text)  # "'Caf\\xe9'"

# Use case:
# repr() - for Python evaluation
# ascii() - for ASCII-only output (logs, APIs)

ascii() vs str()

text = "Hello\nWorld"

# str() - shows representation
str(text)    # Shows actual newline

# ascii() - escapes everything
ascii(text)  # "'Hello\\nWorld'"

# Use case:
# str() - for human display
# ascii() - for ASCII-safe output

Escape Sequence Details

# O(1) - understand escaping rules

# Control characters
ascii("\n")      # "'\\n'"
ascii("\t")      # "'\\t'"
ascii("\r")      # "'\\r'"
ascii("\0")      # "'\\x00'"

# Extended ASCII
ascii("\x7f")    # "'\\x7f'"
ascii("\xff")    # "'\\xff'"

# Unicode BMP (Basic Multilingual Plane)
ascii("α")       # "'\\u03b1'"
ascii("中")      # "'\\u4e2d'"

# Supplementary planes
ascii("𝔸")      # "'\\U0001d538'"

Containers with Unicode

# O(n) - escapes all non-ASCII in container
data = {
    "name": "Josée",
    "city": "Montréal",
    "country": "Québec"
}

ascii(data)
# {'name': 'Jos\\xe9e', 'city': 'Montr\\xe9al', 'country': 'Qu\\xe9bec'}

# Each value is escaped separately
lst = ["café", "naïve", "résumé"]
ascii(lst)
# ['caf\\xe9', 'na\\xefve', 'r\\xe9sum\\xe9']

Performance Patterns

Batch Processing

# O(n * m) - n strings, each ~m length
strings = ["Café", "Naïve", "Résumé"]
ascii_versions = [ascii(s) for s in strings]
# O(n * m)

Large Text

# O(n) - entire text must be scanned
large_text = open("file.txt", "r", encoding="utf-8").read()
safe_version = ascii(large_text)  # O(len(large_text))

# Memory: output may be larger (each non-ASCII becomes \xXX, \uXXXX, etc)

Practical Examples

API Response Logging

# O(n) - log safely without encoding issues
import json

response = {"name": "José", "country": "México"}
response_json = json.dumps(response)

# Log safely in ASCII-only environment
print(ascii(response_json))
# '{"name": "Jos\\u00e9", "country": "M\\u00e9xico"}'

# vs print(response_json) which might have encoding issues

Email Headers

# O(n) - headers must be ASCII
subject = "Meeting: Café ☕ Discussion"

# Make safe for email
safe_subject = ascii(subject)
# "'Meeting: Caf\\xe9 \\u2615 Discussion'"

# Email system can safely handle this

Source Code Comments

# O(n) - include comments with non-ASCII

text = "Author: François"

# Generate comment safely
comment = f"# {ascii(text)}"
# print(comment)
# # 'Author: Fran\\xe7ois'

Special Cases

Empty String

# O(1)
ascii("")  # "''"

Only ASCII

# O(n) - no escaping needed
ascii("abc123!@#")  # "'abc123!@#'"

# Output same as input (with quotes added)

Only Non-ASCII

# O(n) - all characters escaped
ascii("日本語")   # "'\\u65e5\\u672c\\u8a9e'"

# Output is entirely escape sequences

Best Practices

✅ Do:

  • Use ascii() for logging with non-ASCII content
  • Use ascii() for API responses to avoid encoding issues
  • Use ascii() when ASCII-only output is required
  • Use for debugging to see all whitespace and control characters

❌ Avoid:

  • Using ascii() for user-facing output (use str())
  • Assuming ascii() output is smaller (it's usually larger)
  • Using ascii() when you can use proper encoding
  • Forgetting that ascii() doesn't decode escape sequences
  • repr() - Python representation (keeps non-ASCII)
  • str() - String representation (human-readable)
  • encode() - Encode to bytes with specific encoding
  • bytes() - Convert to bytes

Version Notes

  • Python 2.x: Treats strings differently, Unicode handling varies
  • Python 3.x: Consistent Unicode support, uses \uXXXX format
  • All versions: Returns string with quotes, all non-ASCII escaped