是否可以使用exec（）运行缩进块？

Question

Using the exec() python command, is it possible to run indented blocks of code (Like if/else statements or try/except ). For example:

name = input("Enter name: ")
if name == "Bob":
     print("Hi bob")
else:
     print("Hi user")

At the moment I am using this to run the code:

code_list = []
while True:
     code = input("Enter code or type end: ")
     if code == "end":
          break
     else:
          code_list.append(code)
for code_piece in code_list:
     exec(code_piece)

Also I know that this isn't very "Pythonic" or "Good practise" to let the user input their own code but it will be useful in other parts of my code.

Answer 1

The problem here isn't the indentation. The problem is that you're trying to exec the lines of a compound statement one by one. Python can't make sense of a compound statement without the whole thing.

exec the whole input as a single unit:

exec('\n'.join(code_list))

Answer 2

From exec() documentation:

This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed ...

Thus, you can do things like

exec("a=2\nb=3")
exec("if a==2:\n\tprint(a)\nelse:\tprint(b)")

You just need to follow the right syntax and indentation.

Answer 3

Another way of formatting code within an exec() function is to use triple quotes, which makes it easy to see what the code looks like.

code = """                     # Opening quotes
for i in range(0, 10):         # Code line 1         
    print(i)                   # Code line 2
"""                            # Closing quotes
exec(code)

This would maybe not work if you're asking the user to input the code, but it's a trick that may come in handy.