I have a floating point number, say 135.12345678910 . I want to concatenate that value to a string, but only want 135.123456789 . With print, I can easily do this by doing something like:

print "%.9f" % numvar

with numvar being my original number. Is there an easy way to do this?

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With python < 3 (eg 2.6 [see comments] or 2.7), there are two ways to do so.

# Option one 
older_method_string = "%.9f" % numvar

# Option two
newer_method_string = "{:.9f}".format(numvar) 

But note that for python versions above 3 (eg 3.2 or 3.3), option two is preferred.

For more info on option two, I suggest this link on string formatting from the python docs.

And for more info on option one, this link will suffice and has info on the various flags.

UPDATE: Python 3.6 (official release in December of 2016), will add the f string literal, see more info here, which extends the str.format method (use of curly braces such that f"{numvar:.9f}" solves original problem).

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使用一轮：

>>> numvar = 135.12345678910
>>> str(round(numvar,9))
'135.123456789'
>>>

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Python 3.6 | 2017

Just to make it clear, you can use f-string formatting. This has almost the same syntax as the format method, but make it a bit nicer.

Example:

print(f'{numvar:.9f}')

More reading about the new f string:

What's new in Python 3.6(same link as above)

PEP official doc

Python official docs

Really good blog post, talk about performance too:

链接地址: http://www.djcxy.com/p/21370.html

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