#Fibonacci series:
# the sum of two elements defines the next
a, b = 0, 1
while b < 10:
print(b)
a, b = b, a+b
1
1
2
3
5
8
a,b =0,1
while b < 1000:
print(b, end=',')
a, b = b, a+b
- More Control Flow Tools
4.1 if statements
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')
4.2 for statements
#Measure some strings:
words = ['cat', 'window', 'defenestrate']
for w in words:
print(w,len(w))
cat 3
window 6
defenestrate 12
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']
4.3. The range() Function
a = ['Marry','had','a','little','lamb']
for i in range(len(a)):
print(i,a[i])
0 Marry
1 had
2 a
3 little
4 lamb
a = ['Marry','had','a','little','lamb']
for i in range(len(a)):
print(i,a[i])
0 Marry
1 had
2 a
3 little
4 lamb
print(range(10))
range(0, 10)
list(range(5))
[0, 1, 2, 3, 4]
4.4 break and continue Statements, and else Clauses on Loops
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')
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
4.5 pass Statements
空类
class MyEmptyClass:
pass
4.6 Defining Functions
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()
fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
fib
<function fib at 0x03617B28>
f = fib
f(200)
0 1 1 2 3 5 8 13 21 34 55 89 144
