print floating point number

[snippsat]

But going to >>> by entering 'python3', then entering the program name, results in "File

You can not enter python3 in interactive shell.
 python3 is also for Linux command.

Some advice follow my link over and install Python 3.6.
Restart Pc.
Now start cmd,if all work it look like this.

Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. Med enerett.

C:\Windows\System32>cd\

C:\>python
Python 3.6.2 (v3.6.2:5fd33b5, Jul  8 2017, 04:14:34) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

C:\>pip -V
pip 9.0.1 from c:\python36\lib\site-packages (python 3.6)

Now is 3.6 the main version and pip work which is important.
Can still use other version on OS,on Linux is python3 Windows can use py -version shortcut.

C:\>py -3.4
Python 3.4.2 (v3.4.2:ab2c023a9432, Oct  6 2014, 22:15:05) [MSC v.1600 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

C:\>py -2.7
Python 2.7.12 (v2.7.12:d33e0cf91556, Jun 27 2016, 15:19:22) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> exit()

Even install with pip work fine with py shortcut.

C:\>py -3.4 -m pip install requests
Collecting requests
  Downloading requests-2.18.3-py2.py3-none-any.whl (88kB)
    100% |################################| 92kB 1.2MB/s
Collecting chardet<3.1.0,>=3.0.2 (from requests)
  Downloading chardet-3.0.4-py2.py3-none-any.whl (133kB)
    100% |################################| 143kB 1.7MB/s
Successfully installed certifi-2017.7.27.1 chardet-3.0.4 idna-2.5 requests-2.18.3 urllib3-1.22