Python Control Flow Tools
Sección: Programación
Creado: 17-11-24
if
>>> x = int(input("Please enter an integer: "))
Please enter an integer: 42
>>> if x < 0:
... x = 0
... print('Negative changed to zero')
... elif x == 0:
... print('Zero')
... elif x == 1:
... print('Single')
... else:
... print('More')
...
for
>>> # Measure some strings: ... words = ['cat', 'window', 'defenestrate'] >>> for w in words: ... print(w, len(w)) ...
If you need to modify the sequence you are iterating over while inside
>>> for w in words[:]: # Loop over a slice copy of the entire list. ... if len(w) > 6: ... words.insert(0, w) ... >>> words
range
Arithmetic progressions
>>> for i in range(5): ... print(i) ...
range(5, 10) 5 through 9 range(0, 10, 3) 0, 3, 6, 9 range(-10, -100, -30) -10, -40, -70
In many ways the object returned by range() is iterable. We have seen that the for statement is such an iterator. The function list() is another; it creates lists from iterables:
>>> list(range(5)) [0, 1, 2, 3, 4]
break, continue and else
>>> for n in range(2, 10): ... 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 is a prime number 6 equals 2 * 3 7 is a prime number 8 equals 2 * 4 9 equals 3 * 3
>>> for num in range(2, 10):
... if num % 2 == 0:
... print("Found an even number", num)
... continue
... print("Found a number", num)
Found an even number 2
Found a number 3
Found an even number 4
Found a number 5
Found an even number 6
Found a number 7
Found an even number 8
Found a number 9
pass
>>> while True: ... pass # Busy-wait for keyboard interrupt (Ctrl+C)
>>> class MyEmptyClass: ... pass
>>> def initlog(*args): ... pass # Remember to implement this!
Functions
The first statement of the function body can optionally be a string literal; this string literal is the function’s documentation string, or docstring.
>>> def fib(n): # write Fibonacci series up to n ... """Print a Fibonacci series up to n.""" ... a, b = 0, 1 ... while a < n: ... print(a, end=' ') ... a, b = b, a+b ... print() ... >>> # Now call the function we just defined: ... fib(2000) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
>>> fib(0) >>> print(fib(0)) None
>>> def fib2(n): # return Fibonacci series up to n ... """Return a list containing the Fibonacci series up to n.""" ... result = [] ... a, b = 0, 1 ... while a < n: ... result.append(a) # see below ... a, b = b, a+b ... return result ... >>> f100 = fib2(100) # call it >>> f100 # write the result [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
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