python求助

[Sophie Marceau]

前辈们，问一个python问题，图中pi2里面咋有一个小点点，我不懂

[赵4老师]

Format Specification Fields: printf and wprintf Functions

A format specification, which consists of optional and required fields, has the following form:

%[flags] [width] [.precision] [{h | l | I64 | L}]type

Each field of the format specification is a single character or a number signifying a particular format option. The simplest format specification contains only the percent sign and a type character (for example, %s). If a percent sign is followed by a character that has no meaning as a format field, the character is copied to stdout. For example, to print a percent-sign character, use %%.

The optional fields, which appear before the type character, control other aspects of the formatting, as follows:

type

Required character that determines whether the associated argument is interpreted as a character, a string, or a number (see Table R.3).

flags

Optional character or characters that control justification of output and printing of signs, blanks, decimal points, and octal and hexadecimal prefixes (see Table R.4). More than one flag can appear in a format specification.

width

Optional number that specifies the minimum number of characters output. (See printf Width Specification.)

precision

Optional number that specifies the maximum number of characters printed for all or part of the output field, or the minimum number of digits printed for integer values (see Table R.5).

h | l | I64 | L

Optional prefixes to type-that specify the size of argument (see Table R.6).

Precision Specification

The third optional field of the format specification is the precision specification. It specifies a nonnegative decimal integer, preceded by a period (.), which specifies the number of characters to be printed, the number of decimal places, or the number of significant digits (see Table R.5). Unlike the width specification, the precision specification can cause either truncation of the output value or rounding of a floating-point value. If precision is specified as 0 and the value to be converted is 0, the result is no characters output, as shown below:

printf( "%.0d", 0 );      /* No characters output */

If the precision specification is an asterisk (*), an int argument from the argument list supplies the value. The precision argument must precede the value being formatted in the argument list.

The type determines the interpretation of precision and the default when precision is omitted, as shown in Table R.5.

Table R.5   How Precision Values Affect Type

TypeMeaningDefaultc, CThe precision has no effect.Character is printed.d, i, u, o, x, XThe precision specifies the minimum number of digits to be printed. If the number of digits in the argument is less than precision, the output value is padded on the left with zeros. The value is not truncated when the number of digits exceeds precision.Default precision is 1.e, EThe precision specifies the number of digits to be printed after the decimal point. The last printed digit is rounded.Default precision is 6; if precision is 0 or the period (.) appears without a number following it, no decimal point is printed. f The precision value specifies the number of digits after the decimal point. If a decimal point appears, at least one digit appears before it. The value is rounded to the appropriate number of digits. Default precision is 6; if precision is 0, or if the period (.) appears without a number following it, no decimal point is printed.g, GThe precision specifies the maximum number of significant digits printed.Six significant digits are printed, with any trailing zeros truncated.s, SThe precision specifies the maximum number of characters to be printed. Characters in excess of precision are not printed.Characters are printed until a null character is encountered.

If the argument corresponding to a floating-point specifier is infinite, indefinite, or NaN, printf gives the following output.

ValueOutput+ infinity1.#INFrandom-digits– infinity–1.#INFrandom-digitsIndefinite (same as quiet NaN)digit.#INDrandom-digitsNAN digit.#NANrandom-digits

[小石界]

表示小数点