Why Python getcontext().prec = 4 sometimes gives 3 decimals instead of 4? -


I'm new to Python, and this decimal module in my new travel: 

  & gt; & Gt; & Gt; Getcontext () Prec = 4; Print (decimal (7) / decimal (9)); 0.7778 # Everything is OK & gt; & Gt; & Gt; & Gt; & Gt; & Gt; Getcontext () Prec = 4; Print (decimal (2) .sqrt ()); 1.414 # Why not 3 and 4? & Gt; & Gt; & Gt; & Gt; & Gt; & Gt; Getcontext () Prec = 10; & Gt; & Gt; & Gt; Print (decimal (10) .log10 () / decimal (2) .log10 ()); 3.321928094 # Why 9 if set to exact 10? 
 
 Thank you with your attention 
 
 Why did this happen? 
 
 According to estimates: This is the number of important digits: There is also a digit in front of the decimal point. Second and third example (0 in the first example is not significant). 
 
 Note that in the documentation the fourth bullet says: 
 
 
 The decimal module includes a notion of 1.30 + 1.20 2.50 for important locations. 
 
 
 Compare (with your first example, but with a large number): 
 
  & gt; & Gt; & Gt; Getcontext () Prec = 8> gt; & Gt; Print Decimal (7000) / Decimal (9) 777.77778 & gt; & Gt; & Gt; Getcontext () Prec = 4> gt; & Gt; Print Decimal (7000) / Decimal (9) 777.8 & gt; & Gt; & Gt; Getcontext () Prec = 2> gt; & Gt; & Gt; Unfortunately, most examples of documentation are limited to the number of order 1, so this is not clearly shown.

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