[Python编程(第4版)].(Programming.Python.4th.Edition).Mark.Lutz.文字版

5.0

5.0

3.5

0.8

0.8

0.8

6.0

6.0

0.666666666667

4

9.0

4.0

100

3.14159

6.28318

3.334

As usual, we can also test and use the system interactively to work through more of its
utility:

C:\...\PP4E\Lang\Parser> python

>>> import parser1

>>> x = parser1.Parser()

>>> x.parse('1 + 2')

3

Error cases are trapped and reported in a fairly friendly fashion (assuming users think
in zero-based terms):

>>> x.parse('1 + a')

'a' is undefined at column: 4

=> 1 + a

=> ^

>>> x.parse('1+a+2')

'a' is undefined at column: 2

=> 1+a+2

=> ^

>>> x.parse('1 * 2 $')

Lexical Error at column: 6

=> 1 * 2 $

=> ^

>>> x.parse('1 * - 1')

Syntax Error at column: 4

=> 1 * - 1

=> ^

>>> x.parse('1 * (9')

Syntax Error at column: 6

=> 1 * (9

=> ^

>>> x.parse('1 + 2 / 3') # 3.X division change

1.66666666667

>>> x.parse('1 + 2 // 3')

Syntax Error at column: 7

=> 1 + 2 // 3

=> ^

Custom Language Parsers| 1447