6
我想使用AST python模块将python数学表达式转换为postfix表示法。这是我走到这一步:如何使用AST python模块将infix转换为postfix/prefix?
import parser
import ast
from math import sin, cos, tan
formulas = [
"1+2",
"1+2*3",
"1/2",
"(1+2)*3",
"sin(x)*x**2",
"cos(x)",
"True and False",
"sin(w*time)"
]
class v(ast.NodeVisitor):
def __init__(self):
self.tokens = []
def f_continue(self, node):
super(v, self).generic_visit(node)
def visit_Add(self, node):
self.tokens.append('+')
self.f_continue(node)
def visit_And(self, node):
self.tokens.append('&&')
self.f_continue(node)
def visit_BinOp(self, node):
# print('visit_BinOp')
# for child in ast.iter_fields(node):
# print(' child %s ' % str(child))
self.f_continue(node)
def visit_BoolOp(self, node):
# print('visit_BoolOp')
self.f_continue(node)
def visit_Call(self, node):
# print('visit_Call')
self.f_continue(node)
def visit_Div(self, node):
self.tokens.append('/')
self.f_continue(node)
def visit_Expr(self, node):
# print('visit_Expr')
self.f_continue(node)
def visit_Import(self, stmt_import):
for alias in stmt_import.names:
print('import name "%s"' % alias.name)
print('import object %s' % alias)
self.f_continue(stmt_import)
def visit_Load(self, node):
# print('visit_Load')
self.f_continue(node)
def visit_Module(self, node):
# print('visit_Module')
self.f_continue(node)
def visit_Mult(self, node):
self.tokens.append('*')
self.f_continue(node)
def visit_Name(self, node):
self.tokens.append(node.id)
self.f_continue(node)
def visit_NameConstant(self, node):
self.tokens.append(node.value)
self.f_continue(node)
def visit_Num(self, node):
self.tokens.append(node.n)
self.f_continue(node)
def visit_Pow(self, node):
self.tokens.append('pow')
self.f_continue(node)
for index, f in enumerate(formulas):
print('{} - {:*^76}'.format(index, f))
visitor = v()
visitor.visit(ast.parse(f))
print(visitor.tokens)
print()
# 0 - ************************************1+2*************************************
# [1, '+', 2]
# 1 - ***********************************1+2*3************************************
# [1, '+', 2, '*', 3]
# 2 - ************************************1/2*************************************
# [1, '/', 2]
# 3 - **********************************(1+2)*3***********************************
# [1, '+', 2, '*', 3]
# 4 - ********************************sin(x)*x**2*********************************
# ['sin', 'x', '*', 'x', 'pow', 2]
# 5 - ***********************************cos(x)***********************************
# ['cos', 'x']
# 6 - *******************************True and False*******************************
# ['&&', True, False]
# 7 - ********************************sin(w*time)*********************************
# ['sin', 'w', '*', 'time']
我想了解如何将复杂缀数学表达式转换为后缀表达式被送到了一大口C包装,要做到这一点,我试图使用AST模块。
任何人都可以在这里建议吗?
非常感谢你的回答,我没有想过那个,很酷。当你说'如果你想要前缀符号只是交换命令,所以操作符/函数首先被访问,你能否请详细说明一下。',你是什么意思? +1 – BPL
@BPL新增前缀表达式的例子,希望它有帮助! – niemmi
太棒了,谢谢 – BPL