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Getting a map() to return a list in Python 3.x

python
list-comprehension
map-function
performance-optimization
Nikita BarsukovbyNikita Barsukov·Oct 6, 2024
TLDR

Convert map() output to a list in Python 3.x by employing the list() constructor:

# Multiply each item in the list by 2 result = list(map(lambda x: x * 2, [1, 2, 3])) # Because math is fun!

Produces doubled elements: [2, 4, 6].

Transform integers to ASCII characters using:

# Convert integers to ASCII characters, A = 65, B = 66, C = 67 ascii_chars = list(map(chr, [65, 66, 67])) # ABC, easy as 123!

For list of hex values, use:

# Convert integers to hexadecimal, because hex is cooler than decimal hex_values = list(map(hex, [10, 255, 16])) # 10 becomes 'a', 255 is 'ff', 16 is...well...'10'!

And to get a tuple:

# Convert to a tuple instead, because tuples need love too tuple_result = tuple(map(hex, [10, 255, 16])) # Glad we "tuple-d" across this need!

For a tidy map to list conversion by unpacking:

# Using unpacking: cooler, faster, pythonic-er! hex_values_list = [*map(hex, [10, 255, 16])] # Star-power to the rescue!

Alternatively, utilize list comprehensions for clarity:

# With absolutely no hex given comprehension_list = [hex(x) for x in [10, 255, 16]] # Comprehending comprehension is comprehensive!

map versus list comprehension: When to use what

map's benefits and caveats

map() provides:

  • Lazy evaluation: Objects get instantiated only on demand.
  • Efficient memory use: Ideal for large datasets since it doesn't create a list.

But, it's less readable and needs the list() constructor to return a list.

list comprehension's advantages and shortcomings

List comprehensions offer:

  • Readability: They're Pythonic and much appreciated in the community.
  • Flexibility: They allow conditions and complex expressions.
  • Ease: They handle complex transformations without requiring conversion to a list, unlike map().

They, however, create entire lists in memory that may be inefficient for extensive data.

Performance and memory considerations

Compare execution speeds and memory usage of both methods to identify what's best suited to your requirements. Benchmark your data conversion tasks for maximum efficiency.

For ASCII conversions, an efficient approach could be byte manipulation:

# ASCII conversion can be a pain, let's make it efficient ascii_string = bytes([65, 66, 67]).decode('ascii') # Converting bytes to ASCII...Byte me!

Advanced data manipulation

Beyond just ASCII or hex, you can:

  • Filter data: Include or exclude elements based on certain criteria.
  • Modify data: Apply any function to the existing data.
  • Merge data: Combine two lists into tuples.

Filter and merge data with this example:

combined_data = [(x, y) for x in [1, 2] for y in [3, 4] if x != y] # We combine, but not all. Some were...left out!

Lastly, avoid renaming built-ins such as map to prevent confusion.