blocks|key|1820441|text|使用查找表：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1820442|import+operator
ops+=+{+"%2B":+operator.add,+"-":+operator.sub+}+#+etc.

print(ops["%2B"](1,1))+#+prints+2+|code-block|syntax|javascript|1820443|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use a lookup table:
<pre><code>import operator
ops = { &quot;+&quot;: operator.add, &quot;-&quot;: operator.sub } # etc.

print(ops[&quot;+&quot;](1,1)) # prints 2 
</code></pre>

blocks|key|2034101|text|import+operator

ops+=+{
++++'%2B'+:+operator.add,
++++'-'+:+operator.sub,
++++'*'+:+operator.mul,
++++'/'+:+operator.truediv,++#+use+operator.div+for+Python+2
++++'%25'+:+operator.mod,
++++'%5E'+:+operator.xor,
}

def+eval_binary_expr(op1,+oper,+op2):
++++op1,+op2+=+int(op1),+int(op2)
++++return+ops[oper](op1,+op2)

print(eval_binary_expr(*("1+%2B+3".split())))
print(eval_binary_expr(*("1+*+3".split())))
print(eval_binary_expr(*("1+%25+3".split())))
print(eval_binary_expr(*("1+%5E+3".split())))|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2034102|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>import operator

ops = {
 '+' : operator.add,
 '-' : operator.sub,
 '*' : operator.mul,
 '/' : operator.truediv, # use operator.div for Python 2
 '%' : operator.mod,
 '^' : operator.xor,
}

def eval_binary_expr(op1, oper, op2):
 op1, op2 = int(op1), int(op2)
 return ops[oper](op1, op2)

print(eval_binary_expr(*(&quot;1 + 3&quot;.split())))
print(eval_binary_expr(*(&quot;1 * 3&quot;.split())))
print(eval_binary_expr(*(&quot;1 % 3&quot;.split())))
print(eval_binary_expr(*(&quot;1 ^ 3&quot;.split())))
</code></pre>

blocks|key|2034062|text|您可以尝试使用eval()，但是如果字符串不是来自您的，那么这是很危险的。否则，您可以考虑创建一个字典：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2034063|ops+=+{"%2B":+(lambda+x,y:+x%2By),+"-":+(lambda+x,y:+x-y)}|code-block|syntax|javascript|2034064|等等。然后调用|2034065|ops['%2B']+(1,2)|2034066|或者，对于用户输入：|2034067|​|2034068|if+ops.haskey(userop):
++++val+=+ops[userop](userx,usery)
else:
++++pass+#something+about+wrong+operator|2034069|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You can try using eval(), but it's dangerous if the strings are not coming from you.
Else you might consider creating a dictionary:

<pre><code>ops = {"+": (lambda x,y: x+y), "-": (lambda x,y: x-y)}</code></pre>

etc... and then calling <pre><code>ops['+'] (1,2)</code></pre> or, for user input: 

<pre><code>if ops.haskey(userop):
 val = ops[userop](userx,usery)
else:
 pass #something about wrong operator</code></pre>

blocks|key|2034228|text|如果使用查找字典，但使用lambdas而不是运算符库，会怎么样？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2034229|op+=+{'%2B':+lambda+x,+y:+x+%2B+y,
++++++'-':+lambda+x,+y:+x+-+y}|code-block|syntax|javascript|2034230|然后您可以执行以下操作：|2034231|print(op['%2B'](1,2))|2034232|它将输出：|2034233|3|2034234|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

How about using a lookup dict, but with lambdas instead of operator library.

<pre><code>op = {'+': lambda x, y: x + y,
 '-': lambda x, y: x - y}
</code></pre>

Then you can do:

<pre><code>print(op['+'](1,2))
</code></pre>

And it will output:

<pre><code>3
</code></pre>

blocks|key|2034126|text|每个运算符都有一个神奇的方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2034127|OPERATORS+=+{'%2B':+'add',+'-':+'sub',+'*':+'mul',+'/':+'div'}

def+apply_operator(a,+op,+b):

++++method+=+'__%25s__'+%25+OPERATORS[op]
++++return+getattr(b,+method)(a)

apply_operator(1,+'%2B',+2)|code-block|syntax|javascript|2034128|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

There is a magic method corresponding to every operator

<pre><code>OPERATORS = {'+': 'add', '-': 'sub', '*': 'mul', '/': 'div'}

def apply_operator(a, op, b):

 method = '__%s__' % OPERATORS[op]
 return getattr(b, method)(a)

apply_operator(1, '+', 2)
</code></pre>

blocks|key|1820739|text|如果eval()是安全的(不在服务器上等)，请使用它：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1820740|num_1+=+5

num_2+=+10

op+=+['%2B',+'-',+'*']

result+=+eval(f'{num_1}+{op[0]}+{num_2}')

print(result)|code-block|syntax|javascript|1820741|输出:+15|1820742|entityMap^0|2|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Use <code>eval()</code> if it is safe (not on servers, etc):
<pre><code>num_1 = 5

num_2 = 10

op = ['+', '-', '*']

result = eval(f'{num_1} {op[0]} {num_2}')

print(result)
</code></pre>
Output :
15

blocks|key|1820566|text|我知道你想做这样的事情:+5"%2B"7，其中所有3件事都是通过变量传递的，所以示例如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1820567|import+operator

#define+operators+you+wanna+use
allowed_operators={
++++"%2B":+operator.add,
++++"-":+operator.sub,
++++"*":+operator.mul,
++++"/":+operator.truediv}

#sample+variables
a=5
b=7
string_operator="%2B"

#sample+calculation+=>+a%2Bb
result=allowed_operators[string_operator](a,b)
print(result)|code-block|syntax|javascript|1820568|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I understand that you want to do something like:
5"+"7 
where all 3 things would be passed by variables,
so
example:

<pre><code>import operator

#define operators you wanna use
allowed_operators={
 "+": operator.add,
 "-": operator.sub,
 "*": operator.mul,
 "/": operator.truediv}

#sample variables
a=5
b=7
string_operator="+"

#sample calculation =&gt; a+b
result=allowed_operators[string_operator](a,b)
print(result)
</code></pre>

blocks|key|2034195|text|我也遇到了同样的问题，使用Jupyter+Notebook时，我无法导入operator模块。因此，上面的代码帮助我获得了洞察力，但无法在平台上运行。我想出了一种使用所有基本功能的原始方法，它是这样的：(这可以进行大量的改进，但这是一个开始的…)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2034196|#+Define+Calculator+and+fill+with+input+variables
#+This+example+"will+not"+run+if+aplha+character+is+use+for+num1/num2+
def+calculate_me():
++++num1+=+input("1st+number:+")
++++oper+=+input("*+OR+/+OR+%2B+OR+-+:+")
++++num2+=+input("2nd+number:+")

++++add2+=+int(num1)+%2B+int(num2)
++++mult2+=+int(num1)+*+int(num2)
++++divd2+=+int(num1)+/+int(num2)
++++sub2+=+int(num1)+-+int(num2)

#+Comparare+operator+strings+
#+If+input+is+correct,+evaluate+operand+variables+based+on+operator
++++if+num1.isdigit()+and+num2.isdigit():
++++++++if+oper+is+not+"*"+or+"/"+or+"%2B"+or+"-":
++++++++++++print("No+strings+or+ints+for+the+operator")
++++++++else:
++++++++++++pass
++++++++if+oper+is+"*":
++++++++++++print(mult2)
++++++++elif+oper+is+"/":
++++++++++++print(divd2)
++++++++elif+oper+is+"%2B":
++++++++++++print(add2)
++++++++elif+oper+is+"-":
++++++++++++print(sub2)
++++++++else:
++++++++++++return+print("Try+again")

#+Call+the+function
calculate_me()
print()
calculate_me()
print()|code-block|syntax|javascript|2034197|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I was bugged with the same problem, using Jupyter Notebook, I was unable to import the operator module. So the above code helped give me insight but was unable to run on the platform. I figured out a somehwhat primitive way to do so with all the basic funcs and here it is: (This could be heavily refined but it’s a start…)

<pre><code># Define Calculator and fill with input variables
# This example "will not" run if aplha character is use for num1/num2 
def calculate_me():
 num1 = input("1st number: ")
 oper = input("* OR / OR + OR - : ")
 num2 = input("2nd number: ")

 add2 = int(num1) + int(num2)
 mult2 = int(num1) * int(num2)
 divd2 = int(num1) / int(num2)
 sub2 = int(num1) - int(num2)

# Comparare operator strings 
# If input is correct, evaluate operand variables based on operator
 if num1.isdigit() and num2.isdigit():
 if oper is not "*" or "/" or "+" or "-":
 print("No strings or ints for the operator")
 else:
 pass
 if oper is "*":
 print(mult2)
 elif oper is "/":
 print(divd2)
 elif oper is "+":
 print(add2)
 elif oper is "-":
 print(sub2)
 else:
 return print("Try again")

# Call the function
calculate_me()
print()
calculate_me()
print()
</code></pre>

How can I turn a string such as <code>"+"</code> into the operator plus? 
Thanks!

Turn string into operator

如何将"+"这样的字符串转换为加号运算符？谢谢!

问将字符串转换为运算符
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回答 8

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