Python if for else elif while break loop pass control flow tool __python

If statement:
1, if ... elif elif ... else, where else is optional, if and elif have the same indentation, at the end of a line there is a colon

For statement:
2. Unlike C and Pascal, Python's for statement iterates through all the item in the sequence by item

>>> # Measure Some strings:
... words = [' cat ', ' window ', ' defenestrate '] >>> for
W in Words:
  ...     Print (W, Len (w))
...
Cat 3
window 6
defenestrate 12

3. If you need to modify the sequence you are traversing, it is recommended that you first make a copy of the sequence

>>> for W in words[:]:  # Loop over a slice copy of the entire list.
...     If Len (w) > 6:
...         Words.insert (0, W)
...
>>> words
[' defenestrate ', ' Cat ', ' window ', ' defenestrate ']

4, Range () function

>>> for i in Range (5):
.     . Print (i) ...
0
1
2
3
4

The given endpoint end point is never part of the resulting sequence, and range (10) produces 0~9

5, you can specify the starting number of the sequence, tolerance defaults to 1, you can also specify arithmetic progression tolerance
Range (5, 10)
5 through 9

Range (0, 10, 3)
0, 3, 6, 9.

Range (-10,-100,-30)
-10,-40,-70

6, in order to traverse the sequence of the index, you can combine the range () and Len () function:

>>> a = [' Mary ', ' had ', ' a ', ' little ', ' lamb ']
>>> for-I in range (Len (a)):
...     Print (I, a[i])
...
0 Mary
1 had
2 a
3 little
4 lamb

7, Range () return is not a list, but an object, when you traverse it, he will be in order to return to save the space. So when you enter the following statement, there is a strange result:
>>> Print (range (10))
Range (0,10)

8, we say an object is a iterable, that is, an object that needs to get the continuous item to the last function. We see that the for statement is a iterator, and the function list () is another one that is created from iterable lists
>>> List (range (5))
[0, 1, 2, 3, 4]

9. In Python, the ELSE clause is used in conjunction with a loop statement, or a try statement. The front is used to indicate that no break execution is used with a try statement, indicating that no exception occurred
An algorithm to find prime numbers:

>>> for N in range (2):
...     For x in range (2, N):
....         If n% x = = 0:
...             Print (n, ' equals ', X, ' * ', n//x)
...             Break
...     else: ...         # loop fell through without finding a factor
...         Print (n, ' is a prime number ')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 are a prime number
6 equals 2 * 3
7 is a Prime number
8 equals 2 * 4
9 equals 3 * 3

10, the use of the Continue clause is exactly the same as in the C statement

11, the Pass statement does nothing, for a block in syntax requires a statement, but there is no need to perform any action

>>> while True:
...     Pass  # busy-wait for keyboard interrupt (CTRL + C) ...

12, pass can also be used as a placeholder, allowing you to keep thinking more abstract level

>>> def initlog (*args):
...     Pass   # Remember to implement this!
...