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codecs Module Complexity¶

The codecs module provides codec registry and base classes for codec implementations, including character encoding/decoding.

Functions & Methods¶

Operation	Time	Space	Notes
`codecs.encode(obj, encoding)`	O(n)	O(n)	Encode to bytes, n = input size
`codecs.decode(obj, encoding)`	O(n)	O(n)	Decode from bytes
`codecs.open(filename, mode, encoding)`	O(1)	O(1)	Open file with codec
`StreamWriter.write(obj)`	O(n)	O(n)	Encode and write
`StreamReader.read()`	O(n)	O(n)	Read and decode
`getencoder(encoding)`	O(1)	O(1)	Get encoder function
`getdecoder(encoding)`	O(1)	O(1)	Get decoder function
`lookup(name)`	O(1)	O(1)	Registry lookup (amortized)
`register(search_fn)`	O(1)	O(1)	Register codec search function
`unregister(search_fn)`	O(n)	O(1)	n = registry entries
`lookup_error(name)`	O(1)	O(1)	Error handler lookup
`register_error(name, handler)`	O(1)	O(1)	Register error handler
`iterencode(iterable, encoding)`	O(n)	O(1)	Streaming encode
`iterdecode(iterable, encoding)`	O(n)	O(1)	Streaming decode
`getincrementalencoder()`	O(1)	O(1)	Get incremental encoder class
`getincrementaldecoder()`	O(1)	O(1)	Get incremental decoder class
`EncodedFile()`	O(1)	O(1)	Wrap file with recoding
`StreamReaderWriter()`	O(1)	O(1)	Reader/writer wrapper
`StreamRecoder()`	O(1)	O(1)	Transcoding wrapper
`make_encoding_map()`	O(n)	O(n)	n = mapping size
`make_identity_dict()`	O(n)	O(n)	n = mapping size
`charmap_build()`	O(n)	O(n)	Build charmap
`charmap_encode()`	O(n)	O(n)	Encode via charmap
`charmap_decode()`	O(n)	O(n)	Decode via charmap
`ascii_encode/decode`	O(n)	O(n)	Built-in codec helper
`latin_1_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_7_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_8_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_16_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_16_ex_decode`	O(n)	O(n)	Built-in codec helper
`utf_16_le_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_16_be_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_32_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_32_ex_decode`	O(n)	O(n)	Built-in codec helper
`utf_32_le_encode/decode`	O(n)	O(n)	Built-in codec helper
`utf_32_be_encode/decode`	O(n)	O(n)	Built-in codec helper
`unicode_escape_encode/decode`	O(n)	O(n)	Built-in codec helper
`raw_unicode_escape_encode/decode`	O(n)	O(n)	Built-in codec helper
`escape_encode/decode`	O(n)	O(n)	Built-in codec helper
`readbuffer_encode`	O(n)	O(n)	Built-in codec helper
`strict/ignore/replace_errors`	O(n)	O(n)	Error handler helpers
`backslashreplace_errors`	O(n)	O(n)	Error handler helper
`namereplace_errors`	O(n)	O(n)	Error handler helper
`xmlcharrefreplace_errors`	O(n)	O(n)	Error handler helper

Encoding Operations¶

Time Complexity: O(n)¶

Where n = input string size.

import codecs

# Encode string to bytes: O(n)
text = "Hello, 世界" * 1000  # n = 5000 characters

# UTF-8 encoding: O(n)
encoded = codecs.encode(text, 'utf-8')  # O(n)

# ASCII encoding (subset): O(n)
text_ascii = "Hello World" * 1000
encoded = codecs.encode(text_ascii, 'ascii')  # O(n)

# Other encodings: O(n)
encoded = codecs.encode(text, 'utf-16')  # O(n)
encoded = codecs.encode(text, 'latin-1')  # O(n)

Space Complexity: O(n)¶

import codecs

# Output size depends on encoding
text = "Hello, 世界" * 1000

# UTF-8: variable size (1-4 bytes per char)
# Output: O(n), typically 1-2x input
encoded = codecs.encode(text, 'utf-8')  # O(n) space

# UTF-16: fixed 2 bytes per char (+ BOM)
# Output: O(2n)
encoded = codecs.encode(text, 'utf-16')  # O(n) space

# ASCII: 1 byte per char
# Output: O(n)
text_ascii = "Hello" * 1000
encoded = codecs.encode(text_ascii, 'ascii')  # O(n) space

Decoding Operations¶

Time Complexity: O(n)¶

Where n = input bytes size.

import codecs

# Decode bytes to string: O(n)
encoded = b"Hello, \xe4\xb8\x96\xe7\x95\x8c" * 1000

# UTF-8 decoding: O(n)
text = codecs.decode(encoded, 'utf-8')  # O(n)

# ASCII decoding: O(n)
encoded_ascii = b"Hello World" * 1000
text = codecs.decode(encoded_ascii, 'ascii')  # O(n)

# UTF-16 decoding: O(n)
encoded_utf16 = b"\xff\xfeH\x00e\x00l\x00l\x00o\x00" * 1000
text = codecs.decode(encoded_utf16, 'utf-16')  # O(n)

Space Complexity: O(n)¶

import codecs

# Output string size
encoded = b"Hello, \xe4\xb8\x96\xe7\x95\x8c" * 1000

# UTF-8 decoded: variable size
# Output: O(n) for result string
text = codecs.decode(encoded, 'utf-8')  # O(n) space

# UTF-16 decoded: typically smaller
# Output: O(n) for result
text = codecs.decode(encoded, 'utf-16')  # O(n) space

File I/O with Codecs¶

Time Complexity: O(n)¶

Where n = file size.

import codecs

# Open file with encoding: O(1) open + O(n) read/write
with codecs.open('file.txt', 'r', encoding='utf-8') as f:
    # Read and decode: O(n)
    text = f.read()  # O(n) to read and decode

    # Write and encode: O(n)
    # f.write(new_text)  # O(n)

Space Complexity: O(n) or O(k)¶

import codecs

# Full read: O(n) memory
with codecs.open('large.txt', 'r', encoding='utf-8') as f:
    text = f.read()  # O(n) memory

# Streaming read: O(k) memory
with codecs.open('large.txt', 'r', encoding='utf-8') as f:
    while True:
        chunk = f.read(4096)  # O(k) per chunk
        if not chunk:
            break
        process(chunk)

StreamWriter and StreamReader¶

StreamWriter - Encode and Write¶

import codecs

# Create writer: O(1)
writer = codecs.getwriter('utf-8')(open('file.bin', 'wb'))

# Write and encode: O(n)
writer.write("Hello, 世界")  # O(n) to encode
writer.write("More text")  # O(m)

# Total: O(sum of all writes)
writer.close()

StreamReader - Read and Decode¶

import codecs

# Create reader: O(1)
reader = codecs.getreader('utf-8')(open('file.bin', 'rb'))

# Read and decode: O(n)
text = reader.read()  # O(n) to read and decode

# Or read in chunks
reader = codecs.getreader('utf-8')(open('file.bin', 'rb'))
while True:
    chunk = reader.read(4096)  # O(k) per chunk
    if not chunk:
        break

Getting Codec Functions¶

Time Complexity: O(1)¶

import codecs

# Get encoder: O(1) lookup
encoder = codecs.getencoder('utf-8')  # O(1)
result = encoder("Hello")  # O(n) to use

# Get decoder: O(1) lookup
decoder = codecs.getdecoder('utf-8')  # O(1)
result = decoder(b"Hello")  # O(n) to use

# Get reader factory: O(1)
reader_factory = codecs.getreader('utf-8')  # O(1)

# Get writer factory: O(1)
writer_factory = codecs.getwriter('utf-8')  # O(1)

Space Complexity: O(1)¶

import codecs

# Just returns function reference
encoder = codecs.getencoder('utf-8')  # O(1) space
decoder = codecs.getdecoder('utf-8')  # O(1) space

Common Encodings and Performance¶

UTF-8 (Variable-length)¶

import codecs

# Time: O(n) where n = character count
text = "Hello, 世界" * 1000
encoded = codecs.encode(text, 'utf-8')  # O(n)

# Space: 1-4 bytes per character
# ASCII chars: 1 byte
# Most European: 2 bytes
# CJK chars: 3-4 bytes
# Output typically 1-2x input size

UTF-16 (Fixed 2 bytes)¶

import codecs

# Time: O(n)
text = "Hello" * 1000
encoded = codecs.encode(text, 'utf-16')  # O(n)

# Space: Fixed 2 bytes per char + BOM (2 bytes)
# Output: 2n + 2 bytes
# Larger than UTF-8 for ASCII

ASCII (1 byte per char)¶

import codecs

# Time: O(n)
text = "Hello, World" * 1000
encoded = codecs.encode(text, 'ascii')  # O(n)

# Space: Exactly 1 byte per char
# Output: n bytes
# Fastest for ASCII-only text

Latin-1 (1 byte per char)¶

import codecs

# Time: O(n)
text = "Café" * 1000
encoded = codecs.encode(text, 'latin-1')  # O(n)

# Space: Exactly 1 byte per char
# Output: n bytes
# For Western European characters

Error Handling¶

Time Complexity: O(n)¶

import codecs

# Strict mode: O(n), raises on error
text = "Hello, 世界"
try:
    encoded = codecs.encode(text, 'ascii', errors='strict')  # O(n)
except UnicodeEncodeError:
    pass

# Replace mode: O(n)
encoded = codecs.encode(text, 'ascii', errors='replace')  # O(n)
# Non-ASCII becomes '?'

# Ignore mode: O(n)
encoded = codecs.encode(text, 'ascii', errors='ignore')  # O(n)
# Non-ASCII is dropped

# Other modes: O(n)
encoded = codecs.encode(text, 'ascii', errors='xmlcharrefreplace')  # O(n)
# '世' → '&#19990;'

Space Complexity: O(n)¶

import codecs

text = "Hello, 世界"

# Output size depends on error handling
# strict/replace/ignore: O(n)
# xmlcharrefreplace: O(n) or larger
encoded = codecs.encode(text, 'ascii', errors='replace')  # O(n)

Common Patterns¶

Text File Processing¶

import codecs

def process_text_file(filename, input_encoding, output_encoding):
    """Process text file with encoding conversion."""
    # Open and read: O(n)
    with codecs.open(filename, 'r', encoding=input_encoding) as f:
        text = f.read()  # O(n) to read and decode

    # Process: depends on operation
    processed = text.upper()  # O(n)

    # Write with different encoding: O(n)
    with codecs.open(filename + '.out', 'w', encoding=output_encoding) as f:
        f.write(processed)  # O(n) to encode and write

    # Total: O(n)

Streaming with Codecs¶

import codecs

def stream_process(input_file, output_file, from_encoding, to_encoding):
    """Stream process large file with encoding conversion."""
    reader = codecs.getreader(from_encoding)(open(input_file, 'rb'))
    writer = codecs.getwriter(to_encoding)(open(output_file, 'wb'))

    while True:
        chunk = reader.read(4096)  # O(k) per chunk
        if not chunk:
            break

        # Process
        processed = chunk.upper()  # O(k)
        writer.write(processed)  # O(k)

    reader.close()
    writer.close()
    # Total: O(n) time, O(k) memory

Codec Lookup and Registration¶

import codecs

# Get encoder: O(1)
encode_func, decode_func, reader_factory, writer_factory = codecs.lookup('utf-8')

# Use encoder: O(n)
encoded, length = encode_func("Hello, 世界")  # O(n)

# Use decoder: O(n)
decoded, length = decode_func(encoded)  # O(n)

# Use reader/writer factories: O(1)
reader = reader_factory(input_stream)
writer = writer_factory(output_stream)

Performance Characteristics¶

Best Practices¶

import codecs

# Good: Specify encoding explicitly
with codecs.open('file.txt', 'r', encoding='utf-8') as f:
    text = f.read()  # Clear intent

# Avoid: Relying on system encoding
with codecs.open('file.txt', 'r') as f:
    text = f.read()  # May vary by system

# Good: Use appropriate encoding
# UTF-8 for web/general: O(n), 1-4 bytes/char
encoded = codecs.encode(text, 'utf-8')

# Good: Stream large files
reader = codecs.getreader('utf-8')(file_obj)
for chunk in iter(lambda: reader.read(65536), ''):
    process(chunk)  # O(k) memory

# Avoid: Load entire large file
text = reader.read()  # O(n) memory

Encoding Selection¶

import codecs

text = "Sample text 你好"

# UTF-8: Default, universal
# Time: O(n), Space: 1-4 bytes/char
encoded = codecs.encode(text, 'utf-8')

# ASCII: Fastest if text is ASCII-only
# Time: O(n), Space: 1 byte/char
text_ascii = "Hello World"
encoded = codecs.encode(text_ascii, 'ascii')

# Latin-1: For Western European
# Time: O(n), Space: 1 byte/char
text_european = "Café"
encoded = codecs.encode(text_european, 'latin-1')

# UTF-16: For Windows APIs
# Time: O(n), Space: 2 bytes/char
encoded = codecs.encode(text, 'utf-16')

Version Notes¶

Python 2.0+: Basic codecs module
Python 3.0+: Enhanced Unicode support
Python 3.3+: Better error handling
Python 3.7+: Performance improvements

base64 Module - Base64 encoding
io Module - I/O operations with encoding
sys Module - Default encoding/decoding
unicodedata Module - Unicode information

codecs Module Complexity¶

Functions & Methods¶

Encoding Operations¶

Time Complexity: O(n)¶

Space Complexity: O(n)¶

Decoding Operations¶

Time Complexity: O(n)¶

Space Complexity: O(n)¶

File I/O with Codecs¶

Time Complexity: O(n)¶

Space Complexity: O(n) or O(k)¶

StreamWriter and StreamReader¶

StreamWriter - Encode and Write¶

StreamReader - Read and Decode¶

Getting Codec Functions¶

Time Complexity: O(1)¶

Space Complexity: O(1)¶

Common Encodings and Performance¶

UTF-8 (Variable-length)¶

UTF-16 (Fixed 2 bytes)¶

ASCII (1 byte per char)¶

Latin-1 (1 byte per char)¶

Error Handling¶

Time Complexity: O(n)¶

Space Complexity: O(n)¶

Common Patterns¶

Text File Processing¶

Streaming with Codecs¶

Codec Lookup and Registration¶

Performance Characteristics¶

Best Practices¶

Encoding Selection¶

Version Notes¶

Related Documentation¶