understanding yield in python

def gen():
    s = "init string"
    while True:
        s = yield s
        s += " processed"

c= gen()
print(next(c))
print(format(c.send("hello")))

The above has following output

init string
hello processed

when next(c) is called, the gen function runs until line :

s = yield s

However since it does not send anything (using next()), the gen() function only runs the right part of the statement:

yield s

Now when c.send(“hello”) is called, it send “hello” to gen(), and gen() starts to run and s get assiged so at the same line

s = yield s

s is now “hello”, but c.send(“hello”) will need gen() to run until the next yield. In this case, gen() continue runs:

s += "processed"

s now becomes “hello processed”

it continues to run until get the next statement which has yield:

s = yield s

Now the right part of statement is executed, and and c.send(“hello”) returns the “hello processed”.

setup.py vs requirements.txt

Very good and clear document: https://caremad.io/posts/2013/07/setup-vs-requirement/