Summary of Python Yield and Return. until it encounters a StopIteration exception. Every generator is an iterator, but not vice versa. < expr > has to be an expression evaluating to an iterable, from which an iterator will be extracted. 替代内层for循环. An iterator is an object that can be iterated (looped) upon. A Python generator is a function which returns a generator iterator (just an object we can iterate over) by calling yield. annotated_assignment_stmt::= augtarget ":" expression ["=" (starred_expression | yield_expression)] . The return statement returns the value from the function and then the function terminates. The word "yield" has two meanings: to produce something (e.g., to yield corn), and to halt to let someone/thing else… stackoverflow.com send - Python Reference (The Right Way) 0.1 documentation The difference from normal Assignment statements is that only single target is allowed. yield is a keyword in Python that is used to return from a function without destroying the states of its local variable and when the function is called, the execution starts from the last yield statement.Any function that contains a yield keyword is termed as generator. 如果生成器函数需要产出另一个生成器生成的值,传统的解决方法是使用嵌套的for循环: A generator function is like a normal function, instead of having a return value it will have a yield keyword. If a function contains at least one yield statement (it may contain other yield or return statements), it becomes a generator function. Hence, yield is what makes a generator. The yield expression converts the function into a generator to return values one by one. yield may be called with a value, in which case that value is treated as the "generated" value. Python yield vs return. The yield from < expr > statement can be used inside the body of a generator. The yield keyword can be used only inside a function body. A generator is built by calling a function that has one or more yield expressions. A Python generator is a form of coroutine, but has the limitation that it can only yield to its immediate caller. Using the Python "yield" keyword. Annotated assignment statements¶. Python return statement is not suitable when we have to return a large amount of data. Some common iterable objects in Python are – lists, strings, dictionary. The iterator is run to exhaustion, i.e. Performing a file-system search, a user would be happier to receive results on-the-fly, rather the wait for a search engine to go through every single file … Syntactically, yield is a keyword which can be used just like the return keyword, except the return statement terminates the execution of your function and sends back a value to its caller. Create Generators in Python. This means that a piece of code containing a yield cannot be factored out and put into a separate function in the same way as other code. yield from是Python3.3新出现的句法. Motivation. Python Yield vs. Return: Comparison Chart . Both yield and return will return some value from a function. The yieldkeyword behaves like return in the sense that values that "yield from" is available since Python 3.3! It is fairly simple to create a generator in Python. On the whole, yield is a fairly simple statement. 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