for , . , , .
for, while, . . .
python for :
- , {}. “:” . tab .
continue, break, pass - , , . if-else.
for
.
for in :
foreach C++
foreach (type item in set) {};
for i in 'hello world':
print(i * 2, end='')
hheelllloo wwoorrlldd
for - . .
i . , . i .
list_of_lists = [['hammerhead', 'great white', 'dogfish'],[0, 1, 2],[9.9, 8.8, 7.7]]
for list in list_of_lists:
print(list)
['hammerhead', 'great white', 'dogfish']
[0, 1, 2]
[9.9, 8.8, 7.7]
, .
Continue
for . . Continue if, - .
number = 0
for number in range(10):
number = number + 1
if number == 5:
continue
print(str(number))
print('End')
number 0 10 number, . number 5, . :
1
2
3
4
6
7
8
9
10
End
Break
if. .
number = 0
for number in range(10):
number += 1
if number == 5:
break
print('Number = ' + str(number))
print('Out of loop')
if : number 5, . print()
Number = 5.
break, print().
.
for n in range(2, 10):
for x in range(2, n):
if n % x == 0:
print(n, 'equals', x, '*', n//x)
break
else:
print(n, 'is a prime number')
. 2 10 n. n 2 n. , 8 . x. if , n / x . true, , . n / x , .
Pass
.
number = 0
for number in range(10):
number += 1
if number == 5:
pass
print(str(number))
print('End')
, if number == 5 .
1
2
3
4
5
6
7
8
9
10
End
, pass . , . , , .
class MyClass(object):
def meth_a(self):
pass
def meth_b(self):
print "I'm meth_b"
meth_a . Python , if, except, def, class . .
IndentationError: expected an indented block.
pass.
class CompileError(Exception):
pass
pass - .
for pass:
for t in range(25):
do(t)
if t == 20:
pass
0 25. t. do(). , , pass. , do 24 t = 20.
for .
:
for i in [0, 1, 2, 3, 4, 5]:
print i**2
, .
array = [1, 2, 3, 4, 5, 6, 7, 8, 9]
for in array:
print i
array = [1, 2, 3, 4, 5, 6, 7, 8, 9]
, range(). range() : , , . . , range(5) , 0 5. , .
range(0, 10, 2)
:
0, 2, 4, 6, 8, 10
. ,
colors = ['red', 'green', 'blue', 'yellow']
, , .
for i in range(len(colors)):
print colors[i]
, for :
colors = ['red', 'green', 'blue', 'yellow']
for color in colors:
print color
, reversed().
colors = ['red', 'green', 'blue', 'yellow']
for color in reversed(colors):
print color
. , .
enumerate() . python for.
. enumerate() :
for i in range(len(L)):
item = L[i]
len(). , , L. , range(). [0, … n].
L[i] L.
L[0], L[1], L[2] ..
enumerate() b
for counter, value in enumerate(L):
print(“index : “counter, “value : “value)
Enumerate() -, for .
items() iteritems(), .
d.items()
d.iteritems()
, zip().
A B, zip-, . A B .
zip_object[1] = [A[1], B[1]];
zip() 4 , - 4 . . , -.
, , , zip_longest().
list(itertools.zip_longest((1,2,3), [4]))
, , keys().
.
for k in d.keys():
if k.startswith('R'):
del d[k]
d. keys(). k. startswith, .
startswith() , . : prefix, start, end.
str.startswith(prefix[, start[, end]]) -> bool
- prefix. .
my_str.startswith(‘value’)
my_str.startswith((‘value1’, ‘value2’))
, ().
start , . . start = -x, x . end , . . end = -x x .
startswith() endswith(). , . suffix, start, end, .
, - dict(izip( 1, 1)). , :
‘ 1’ : ‘ 2’
names = ['raymond', 'rachel', 'matthew']
colors = ['red', 'green', 'blue']
d = dict(zip(names, colors))
dict() , - “:”. 2. , - 1.
d[‘raymond’]
, , get().
d.get(key, default = None)
d key, key[index].
colors = ['red', 'green', 'red', 'blue', 'green', 'red']
d = {}
for color in colors:
d[color] = d.get(color, 0) + 1
get() .
colors = ['red', 'green', 'red', 'blue', 'green', 'red']
d = {}
for color in colors:
if color not in d:
d[color] = 0
d[color] += 1
for.