CODEWITHSUNDEEP
pythonlistpython-3.x
RegDoe
RegDoe

Reputation: 35

Formatting lists of objects in python

I have read a lot of similar questions related to my question, but I have not seen any specifically for this. I have a list of objects, such as 

l = ((a, 0.5), (b, 0.75), (c, 0.954367))

I want to be able to print out only the numbers, formatted to 5 decimal places. I was not too sure how to go about this, so I started by trying to slice it and then print it as such

nums = list(z[1:2] for z in l)    # originally had 'tuple' instead of 'list'
print("numbers: {:.5f}".format(nums))

The slicing works, giving me only the numbers, but when I get to the print statement I get an error 

TypeError: non-empty format string passed to object.__format__

I originally had the slicing to be done as a tuple, but thought that that may have been causing the error so changed it to a list, which did not help. One answer I read noted that "bytes objects do not have a _ _format__ method of their own, so the default from object is used." and suggested converting it to a string instead - which resulted in the same error.

My question essentially, is there a way to fix this error, or a better way to get the output without slicing/using the method above?

Thank you,

Upvotes: 1

Views: 4377

Answers (3)

AMIT KUMAR SHARMA
AMIT KUMAR SHARMA

Reputation: 1

try:

nums = list(z[1] for z in l)

z[1:2] essentially gives another list of numbers: [[0.5],[0.75],[0.954367]], which I don't think you require.

Upvotes: -1

Dimitris Fasarakis Hilliard
Dimitris Fasarakis Hilliard

Reputation: 160567

You're trying to use a float presentation type, 'f', with a list object. That's the cause of the failure.

Supply print with a list comprehension of the formatted values which you can unpack and provide as positionals:

print("numbers: ", *["{0[0]:.5f}".format(i) for i in nums])

This now prints out:

numbers:  0.50000 0.75000 0.95437

Upvotes: 1

Ahasanul Haque
Ahasanul Haque

Reputation: 11134

Use simple list comprehension.

>>> l = (('a', 0.5), ('b', 0.75), ('c', 0.954367))
>>> ["{:.5f}".format(i[1]) for i in l]
[ '0.50000', '0.75000', '0.95437']

Upvotes: 1

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