[英]what's different between these two simple python codes? (one works and the other doesn't work)
[英]PuLP doesn't work with one list but works with another. What is the difference between these two?
我是 python 的新手,因為優化而選擇了它,我想學習一些新東西。 我使用 PyQt5 和 PuLP 制作了一個 lp 求解器程序。 這個概念很簡單:用戶在 QTextEdit 小部件中輸入 Lp 問題,然后單擊求解按鈕,然后在 QTextBrowser 中獲取結果。
我正在使用並嘗試復制的示例練習:
prob = LpProblem("LP problem", LpMaximize)
x1 = LpVariable("x1", lowBound=0, cat='Integer') # Integer variable x1 >= 0
x2 = LpVariable("x2", lowBound=0, cat='Integer') # Integer variable x2 >= 0
prob += x2<=4
prob += 4*x1 + 2*x2 <= 20
prob += 1*x1 + 4*x2 <= 12
prob += 4*x1 + 4*x2
prob.solve()
這種方式就像一個魅力。 按鈕的 function:
def textToVar(self):
prob = LpProblem("LP problem", LpMaximize)
x1 = LpVariable("x1", lowBound=0, cat='Integer') # Integer variable x1 >= 0
x2 = LpVariable("x2", lowBound=0, cat='Integer') # Integer variable x2 >= 0
mytext = self.lpInput.toPlainText()
split = mytext.splitlines()
for ele in range(0, len(split)):
prob += split[ele]
prob.solve()
for v in prob.variables():
self.lpOutput.append(str(v.name) + ' = ' + str(v.varValue))
vmax = (value(prob.objective))
self.lpOutput.append('max = ' + str(vmax))
它不起作用,我認為這是因為split = mytext.splitlines()
生成['x2<=4', '4*x1+2*x2<=20', '1*x1+4*x2<=12', '4*x1+4*x2']
而不是[x2<=4, 4*x1+2*x2<=20, 1*x1+4*x2<=12, 4*x1+4*x2]
。 如何將我的列表從第一個轉換為第二個? 也許我可以使用另一種方法將輸入存儲在列表或變量中,而不是splitlines()
?
先感謝您!
您可以使用exec()
,就像@AirSquid 在他們的評論中指出的那樣,但這確實會引發安全問題。 另一種方法是解析字符串,因為您知道它們將包含什么。 然后,如果出現意外情況,您很容易拋出錯誤。
import re
import pulp as pl
x1 = pl.LpVariable("x1", lowBound=0, cat='Integer') # Integer variable x1 >= 0
x2 = pl.LpVariable("x2", lowBound=0, cat='Integer') # Integer variable x2 >= 0
def parse_equation(string):
string_parts = re.split("(<=|=|>=)", string)
if len(string_parts) == 1:
# Objective function
return parse_equation_part(string_parts[0])
if len(string_parts) != 3:
raise Exception(f"Unexpected number of parts in {string_parts}")
lhs, comparator, rhs = (
parse_equation_part(string_parts[0]),
string_parts[1],
parse_equation_part(string_parts[2])
)
if comparator == "<=":
return lhs <= rhs
if comparator == ">=":
return lhs >= rhs
return lhs == rhs
def parse_equation_part(string):
addition_parts = re.split("(\+|-)", string)
result = parse_addition_part(addition_parts.pop(0))
while addition_parts:
symbol, addition_part, addition_parts =\
addition_parts[0], addition_parts[1], addition_parts[2:]
part_result = parse_addition_part(addition_part)
if symbol not in ('+', '-'):
raise Exception(f"Unexpected value {symbol}")
if symbol == '-':
result -= part_result
else:
result += part_result
return result
def parse_addition_part(string):
parts = string.split("*")
result = 1
for part in parts:
if part == 'x1':
result *= x1
elif part == 'x2':
result *= x2
elif part.isnumeric():
result *= float(part)
else:
raise Exception(f"Unexpected part {part}, expected number or x1/x2")
return result
for s in ['x2>=4', '4*x1+2*x2=20', '1*x1-4*x2<=12', '4*x1+4*x2']:
print(s.ljust(20, ' '), '->', parse_equation(s))
產量
x2>=4 -> x2 >= 4.0
4*x1+2*x2=20 -> 4.0*x1 + 2.0*x2 = 20.0
1*x1-4*x2<=12 -> x1 - 4.0*x2 <= 12.0
4*x1+4*x2 -> 4.0*x1 + 4.0*x2
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