在 Python 中同时赋值和打印

Question

In Python, is there a way to assign a result to a variable and immediately print it? In other words, I am looking for a one-line equivalent to

a = something()
print(a)

(just once, not every assignment should be automatically printed).

There are REPLs, eg for Scala, where this happens automatically:

scala> val count = 1
count: Int = 1

Answer 1

Well, if you just want to create a new variable and print the value of that variable like you've shown us, you could have a simple function to print and return the value:

def print_and_return(value):
    print(value)
    return value

And now you can use it like this:

>>> a = print_and_return(5)
5
>>> print(a)
5

---

An other way, which you should never use, is to use the globals() dict.

I repeat, you should never do this.

def print_and_set(name, value):
    globals()[name] = value
    print(globals()[name])

Now you can call it using:

print_and_set('a', 5)

And it will print 5 and you can also access the variable a in the global namespace.

Answer 2

从技术上讲，这是一行：

a = something(); print(a)

Answer 3

This is missing from python and for a good reason i guess. In C you could have a valid statement like if a=30 { ... } because any assignment statement would have the assigned value , which could lead someone seeing the code for the first time scratching their heads.

Also, baking your own assign function would be problematic since you get a reference copy inside the function body and not the actual variable

TL;DR; -> no, there isn't

Answer 4

Technically you can "print" and assign on the same line by using sys. See the following:

>>> import sys
>>> a = sys.stdout.write("hello")
hello
>>> print(a)
5

As you can see, you "print" - by writing to standard out which is essentially the the same as print() - the string and assign the length of the string to the variable - not the string itself.

Answer 5

As of Python 3.8, the answer to this has changed. Now, you can assign a value to a variable and return that same value using "assignment expressions" (colloquially called "the Walrus operator").