# Python | yield Keyword

`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. Hence, yield is what makes a generator. yield keyword in Python is less known off but has a greater utility which one can think of.

Code #1 : Demonstrating yield working

 `# Python3 code to demonstrate  ` `# yield keyword ` ` `  `# generator to print even numbers ` `def` `print_even(test_list) : ` `    ``for` `i ``in` `test_list: ` `        ``if` `i ``%` `2` `=``=` `0``: ` `            ``yield` `i ` ` `  `# initializing list  ` `test_list ``=` `[``1``, ``4``, ``5``, ``6``, ``7``] ` ` `  `# printing initial list ` `print` `(``"The original list is : "` `+`  `str``(test_list)) ` ` `  `# printing even numbers  ` `print` `(``"The even numbers in list are : "``, end ``=` `" "``) ` `for` `j ``in` `print_even(test_list): ` `    ``print` `(j, end ``=` `" "``) `

Output :

```The original list is : [1, 4, 5, 6, 7]
The even numbers in list are :  4 6
```

Code #2:

 `# A Python program to generate squares from 1  ` `# to 100 using yield and therefore generator  ` ` `  `# An infinite generator function that prints  ` `# next square number. It starts with 1  ` `def` `nextSquare():  ` `    ``i ``=` `1``;  ` ` `  `    ``# An Infinite loop to generate squares  ` `    ``while` `True``:  ` `        ``yield` `i``*``i                  ` `        ``i ``+``=` `1` `# Next execution resumes  ` `                ``# from this point      ` ` `  `# Driver code  ` `for` `num ``in` `nextSquare():  ` `    ``if` `num > ``100``:  ` `        ``break`     `    ``print``(num)  `

Output:

```1
4
9
16
25
36
49
64
81
100```

• Since it stores the local variable states, hence overhead of memory allocation is controlled.
• Since the old state is retained, flow doesn’t start from the beginnning and hence saves time.

• Sometimes, the use of yield becomes erroneous is calling of function is not handled properly.
• The time and memory optimization has a cost of complexity of code and hence sometimes hard to understand logic behind it.

Practical Applications:
The possible practical application is that when handling the last amount of data and searching particulars from it, `yield `can be used as we don’t need to lookup again from start and hence would save time. There can possibly be many application of yield depending upon the use cases.

 `# Python3 code to demonstrate yield keyword ` ` `  `# Checking number of occurrence of  ` `# geeks in string  ` ` `  `# generator to print even numbers ` `def` `print_even(test_string) : ` `    ``for` `i ``in` `test_string: ` `        ``if` `i ``=``=` `"geeks"``: ` `            ``yield` `i ` ` `  `# initializing string ` `test_string ``=` `" The are many geeks around you, \ ` `              ``geeks are known ``for` `teaching other geeks" ` ` `  `# printing even numbers using yield ` `count ``=` `0` `print` `(``"The number of geeks in string is : "``, end ``=` `"" ) ` `test_string ``=` `test_string.split() ` ` `  `for` `j ``in` `print_even(test_string): ` `    ``count ``=` `count ``+` `1` ` `  `print` `(count) `

Output :

`The number of geeks in string is : 3`

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