Formatting string to certain character limit in Python

Question

I have a code that outputs a whole bunch of numbers after doing some maths on them. At one point in the code they are rounded off with numpy.rint, and in certain cases (I believe when a 9 is rounded to a 10) I end up with a trailing zero that I do not want. I have some code that looks sort-of like this

ra3n = ra3/60 * 10
ra3n = np.rint(ra3n)
ra3n = ra3n.astype(str) ##there is a good reason that this needs to be a string

I need all of the resulting ra3n to be 5 characters long, but occasionally one pops out as 6 characters long. How would I format this properly? Keep in mind I'm a total python noob, so I might need it spelled out for me =)

EDIT:

Here's my output:

00244-2451
00244-2702
00278-0629
00286-1614
00295-1101
002910-0546
00303+0711
00305+2246
00348+2604
003410+0423
00355-0204
00359+1236
00360-0931
00386-1210

The instances where there are six digits instead of 5 in the first half of the string are the erroneous ones; those trailing zeroes should not be there.

ra3n.astype('|S5')?

user2285236
– user2285236

2016-05-10 19:38:18 +00:00
Commented May 10, 2016 at 19:38 — user2285236
– user2285236, Commented May 10, 2016 at 19:38
Attempted this, but it didn't work.

uhurulol
– uhurulol

2016-05-10 19:57:19 +00:00
Commented May 10, 2016 at 19:57 — uhurulol
– uhurulol, Commented May 10, 2016 at 19:57

conner.xyz · Accepted Answer · 2016-05-10 19:12:47Z

2

ra3n = ra3n[:-1] if ra3n[-1] == '0' else ra3n

There's probably a better solution, but I'm not sure I really understand your issue without seeing some output.

answered May 10, 2016 at 19:12

conner.xyz

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1 Comment

uhurulol Over a year ago

Edited with my output.

Rory Daulton · Accepted Answer · 2016-05-10 19:49:06Z

2

You change the type of ra3n, which is poor programming practice. Try this.

ra3n = format(ra3/60.*10., '5f')[:5]

This gives exactly five characters. Note that if the string would usually be six characters long, this cuts off the last character, for good or for bad. Note also that I included decimal points in the 60 and 10 numbers: this guarantees that floating-point division will be used, rather than integer division if this is done in Python 2.

edited May 10, 2016 at 19:49

answered May 10, 2016 at 19:19

Rory Daulton

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6 Comments

uhurulol Over a year ago

Okay, cool. I'm having a problem though: I use numpy.loadtxt to import my arrays, and I have to import as str because there are a bunch of different data types. So I then use ra3 = ra3.astype(float) just before the line you suggested, but it's giving me Unknown format code 'f' for object of type 'str' for the line you gave me.

Rory Daulton Over a year ago

@uhurulol: Oops, I had a typo: I wrote r13 rather than ra3. Try it now. Or perhaps use format(float(ra3)/60.*10., '5f')[:5].

uhurulol Over a year ago

I got that typo don't worry, but it's still not working ><

uhurulol Over a year ago

The second suggestion you made gives this error: TypeError: only length-1 arrays can be converted to Python scalars

Rory Daulton Over a year ago

@uhurulol: I don't know numpy, so I am not sure what is happening, I can only guess. What exactly is the type of ra3?

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