def yrange(n):
    i = 0
    while i < n:
        yield i
        i += 1

>>> def foo():
...     print("begin")
...     for i in range(3):
...         print("before yield", i)
...         yield i
...         print("after yield", i)
...     print("end")
...
>>> f = foo()
>>> next(f)
begin
before yield 0
0
>>> next(f)
after yield 0
before yield 1
1
>>> next(f)
after yield 1
before yield 2
2
>>> next(f)
after yield 2
end
Traceback (most recent call last):
  File "<pyshell#13>", line 1, in <module>
    next(f)
StopIteration
>>>

f_2 = foo()
for i in f_2: print(i)

begin
before yield 0
0
after yield 0
end
before yield 1
1
after yield 1
end
before yield 2
2
after yield 2
end

def yrange():
    i = 1
    while True:
        yield i
        i = i + 1

def squares():
    for i in yrange():
        yield i * i

def take(n, seq):
    seq = iter(seq)
    result = []
    try:
        for i in range(n):
            result.append(next(seq))
    except StopIteration:
        pass
    return result

print(take(5, squares()))

# [1, 4, 9, 16, 25]

def fib(n):
    if n <= 1:
        return 1
    a, b = 0, 1
    for _ in range(n):
        a, b = b, a + b
        yield a

for i in fib(10):
    print(i, end=' ')

# Result：1 1 2 3 5 8 13 21 34 55 

generator_expressions = (x for x in range(10))
generator_expressions
<generator object <genexpr> at 0x0000023F8BC51AF0>
sum(generator_expressions)
45

a = range(5)
print(list(a))
[0, 1, 2, 3, 4]

def infinite_sequence():
    num = 0
    while True:
        yield num
        num += 1

def csv_reader(file_name):
    file = open(file_name)
    result = file.read().split("\n")
    return result

csv_gen = csv_reader("some_file.csv")
row_count = 0

for row in csv_gen:
    row_count += 1

print(f"Row count is {row_count}")

def csv_reader(file_name):
    for row in open(file_name, "r"):
        yield row

def readfiles(filenames):
    for f in filenames:
        for line in open(f):
            yield line

def grep(pattern, lines):
    return (line for line in lines if pattern in line)

def printlines(lines):
    for line in lines:
        print(line, end="")

def main(pattern, filenames):
    lines = readfiles(filenames)
    lines = grep(pattern, lines)
    printlines(lines)

def isPrime(n):
    if n < 2 or n % 1 > 0:
        return False
    elif n == 2 or n == 3:
        return True
    for x in range(2, int(n**0.5) + 1):
        if n % x == 0:
            return False
    return True

def getPrimes():
    value = 0
    while True:
        if isPrime(value):
            i = yield value
            if i is not None:
                value = i
        value += 1

prime_gen = getPrimes()
print(next(prime_gen))
print(prime_gen.send(1000))
print(next(prime_gen))

prime_gen = getPrimes()

for x in prime_gen:
    if x > 20:
        prime_gen.throw(ValueError, "I think it was enough!")
    print(x)

prime_gen = getPrimes()

for x in prime_gen:
    if x > 20:
        prime_gen.close()
    print(x)