Renesh Bedre

Renesh Bedre

Bioinformatics Scientist

New good features in Python 3.9

Renesh Bedre     1 minute read   Follow @renbedre

  • Python 3.9 is still in development and expected to release final version on October 2020
  • Currently, 3.9.0a6 version is available for download as of April 29, 2020
  • Note: Here, I have covered some of the major features of Python 3.9 and a complete list of of all features can found here

Merge two dictionaries (dicts) using union operators

# I am using interactive python interpreter (Python 3.9.0a6)
# create two dicts
>>> d1 = {1: 'one', 2: 'two', 3: 'three'}
>>> d2 = {4: 'four', 5: 'five', 6: 'six'}

# merge two dicts in python 3.9
>>> d1 | d2
{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six'}

# merge two dicts in python (3.5 to 3.8)
>>> {**d1, **d2}
{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six'}

Update dictionaries (dicts) union operators

# update current dict with key-values from other dict (like appending the dict)
>>> d1 = {1: 'one', 2: 'two', 3: 'three'}
>>> d2 = {4: 'four', 5: 'five', 6: 'six'}

# update d1 in python 3.9
>>> d1 |= d2
>>> d1
{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six'}

# in python 3.8
>>> d1 = {1: 'one', 2: 'two', 3: 'three'}
>>> d2 = {4: 'four', 5: 'five', 6: 'six'}

>>> d1.update(d2)
>>> d1
{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five', 6: 'six'}

String methods (removeprefix() and removesuffix() )

# in python 3.9
>>> s = 'python_390a6'

# apply removeprefix()
>>> s.removeprefix('python_')
'390a6'

# apply removesuffix()
>>> s = 'python.exe'
>>> s.removesuffix('.exe')
'python'

# in python 3.8 or before
>>> s = 'python_390a6'
>>> s.lstrip('python_')
'390a6'

>>> s = 'python.exe'
>>> s.rstrip('.exe')
'python'

Note: removeprefix() and removesuffix() string methods added in Python 3.9 due to issues associated with lstrip and rstrip interpretation of parameters passed to them. Read PEP 616 for more details

math functions

# in python 3.9
math.gcd() function can take more than two arguments
math.lcm(*integers), math.ulp(x), and math.nextafter(x, y) functions added

Check detailed usage

# in python 3.9
>>> from pathlib import Path
>>> p = Path('/some/path/for/symlink_file')
>>> p.symlink_to('/some/path/for/existing_file')
# get the path for existing_file to which symlink_file points to
>>> p.readlink()
# should get PosixPath('/some/path/for/existing_file')

References

  • https://docs.python.org/3.9/whatsnew/3.9.html
  • https://www.python.org/dev/peps/pep-0596/
  • https://www.python.org/dev/peps/pep-0584
  • https://www.python.org/dev/peps/pep-0616
  • https://docs.python.org/3.9/library/math.html

Last updated: May 1, 2020

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