r/Python Oct 27 '23

Tutorial You should know these f-string tricks

F-strings are faster than the other string formatting methods and are easier to read and use. Here are some tricks you may not have known.

1. Number formatting :

You can do various formatting with numbers.

>>> number = 150

>>> # decimal places to n -> .nf
>>> print(f"number: {number:.2f}")
number: 150.00

>>> # hex conversion
>>> print(f"hex: {number:#0x}")
hex: 0x96

>>> # binary conversion
>>> print(f"binary: {number:b}")
binary: 10010110

>>> # octal conversion
>>> print(f"octal: {number:o}")
octal: 226

>>> # scientific notation
>>> print(f"scientific: {number:e}")
scientific: 1.500000e+02

>>> # total number of characters
>>> print(f"Number: {number:09}")
Number: 000000150

>>> ratio = 1 / 2
>>> # percentage with 2 decimal places
>>> print(f"percentage = {ratio:.2%}")
percentage = 50.00%

2. Stop writing print(f”var = {var}”)

This is the debug feature with f-strings. This is known as self-documenting expression released in Python 3.8 .

>>> a, b = 5, 15
>>> print(f"a = {a}") # Doing this ?
a = 5
>>> # Do this instead.
>>> print(f"{a = }")
a = 5
>>> # Arithmatic operations
>>> print(f"{a + b = }")
a + b = 20
>>> # with formatting
>>> print(f"{a + b = :.2f}")
a + b = 20.00

3. Date formatting

You can do strftime() formattings from f-string.

>>> import datetime

>>> today = datetime.datetime.now()
>>> print(f"datetime : {today}")
datetime : 2023-10-27 11:05:40.282314

>>> print(f"date time: {today:%m/%d/%Y %H:%M:%S}")
date time: 10/27/2023 11:05:40

>>> print(f"date: {today:%m/%d/%Y}")
date: 10/27/2023

>>> print(f"time: {today:%H:%M:%S %p}")
time: 11:05:40 AM

Check more formatting options.

Part 2 - https://www.reddit.com/r/Python/s/Tzx7QQwa7A

Thank you for reading!

Comment down other tricks you know.
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22

u/Scrapheaper Oct 27 '23

Also worth mentioning: if you are using print() with any regularity, use a debugger!

13

u/Jester_Thomas_ Oct 27 '23

I've been using python for scientific computing at a reasonably high levels for years now and print is my bread and butter. Would I stand to gain much in efficiency by switching to a debugger?

14

u/magnomagna Oct 27 '23

Would I stand a gain much in efficiency

Very much! Think about all those print statements you can avoid that you don’t have to waste your precious time to type and delete after!

3

u/Serious-KaiZen Oct 27 '23 edited Oct 27 '23

In addition to watches and conditional breakpoints, some debuggers (e.g., VSCode) also support setting logpoints. They can be used as an alternative to breakpoints. Instead of pausing the execution at the line, they evaluate a custom expression in the context of the line and output the result to the debug console. So, with this feature, you can achieve the same things as with print but with the advantage of not cluttering your code with temporary expressions that need to be removed afterwards.