Float to string general format

Question

Python keeps using fixed format for large floats:

>>> str(1.0e-2)
'0.01'
>>> str(1.0e+2)
'100.0'
>>> str(1.0e-10)
'1e-10'
>>> str(1.0e+10)
'10000000000.0'

How can I make it print 1e+10 in the last case, similar to c++:

std::cout << 1.0e-2 << '\n'
          << 1.0e+2 << '\n'
          << 1.0e-10 << '\n'
          << 1.0e+10 << '\n';

0.01
100
1e-10
1e+10

I don't want to always use scientific notation.

How do I make Python conversion behave similar to C++ general format for

str(x)

when x is a float?

"%.2e" % 1e-10

user12675132
– user12675132

2020-02-22 13:55:57 +00:00
Commented Feb 22, 2020 at 13:55 — user12675132
– user12675132, Commented Feb 22, 2020 at 13:55

Johan · Accepted Answer · 2020-02-22 13:57:22Z

3

You can do this with scientific notation

"{:e}".format(1.0e-7)

Or you can choose how many digits to show after the decimal by adding .n before the e

"{:.2e}".format(1.0e-7)

answered Feb 22, 2020 at 13:57

Johan

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3 Comments

user2052436 Over a year ago

I don't want to always use scientific notation: it will print '1.000000e+02' instead of 100. Float comes in a variable and it may be 100.0 or 1e+10. How do I make it behave like C++ example?

kaya3 Over a year ago

I think the C++ std::to_string function isn't specified so exactly; just choose a bound (say, 1e9) and write something like ('{:e}' if abs(x) >= 1e9 else '{}').format(number).

Johan Over a year ago

@user2052436 See my other example in my post where you can set the precision of the representation. But if you want to have a custom precision for when to use scientific notation you could just use if conditions for when to format with scientific notation or not.

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