30.html ( File view )

  • By 2010-08-21
  • View(s):12
  • Download(s):0
  • Point(s): 1
			






Safari | Python Developer's Handbook -> Control Statements





< BACKMake Note | BookmarkCONTINUE >
152015024128143245168232148039199167010047123209178152124239215162145080038237082193198183

Control Statements

Python implements all the necessary types of control statements that your program might require. The syntax provided by Python's if, for, and while statements should be enough for your needs.

Tip

Remember to type a colon at the end of each line where you enter a statement declaration.



if/elif/else

The general syntax for the if/elif/else statement is as follows:

						
1: if <condition>:
2:     <statements>
3: [elif <condition>:
4:     <statements>]
5: [elif <condition>:
6:     pass]
7: 
8: [else:
9:     <statements>]

					

Note that both elif and else clauses are optional. As you can see in lines 3 through 7, it is only necessary to use elif when you need to handle multiple cases. That is exactly how you implement the switch/case statements from other languages.

Line 6 introduces you to an empty clause that does nothing. It is called pass.

for

The for statement implements loops within a sequence (list). Each element in the sequence assigns its value to variable on its turn. The general syntax is as follows:

						
for <variable> in <sequence>:
    <statements>
[else:
    <statements>]

					

The else clause is only executed when the for statement isn't executed at all, or after the last loop has been executed. In other words, the else statement is always executed unless the break statement is executed inside the loop.

Let's see some examples:

						
>>> for n in [1,2,3,4,5]:
       print n,

1, 2, 3, 4, 5
>>> t = [(1,2),(2,4),(3,6)]
>>> for t1, t2 in t:
       print t1, t2

1 2
2 4
3 6
				
					

while

The while statement implements a loop that executes the statements while the condition returns true.

						
while <condition>:
     <statements>
[else:
     <statements>

					

The else clause is only executed when the while statement isn't executed at all, or after the last loop has been executed. In other words, the else statement is always executed unless the break statement is executed inside the loop.

The following example demonstrates the use of the while statement:

						
>>> x = 5
>>> while x > 0:
       print x,
       x = x-1

5 4 3 2 1

					

The next example implements an infinite loop because the pass statement does nothing and the condition will always be true.

						
>>> while 1:
       pass
				
					

break/continue

Next are two commands that can be used inside for and while types of loop.

break

The break clause exits a loop statement without executing the else clause.

							
>>> for n in [1, 2, 3]:
     print n,
     if n == 2:
         break
 else:
     print "done"

1 2

						
continue

The continue clause skips the rest of the loop block, jumping all the way back to the loop top.

							
>>> x = 5
>>> while x > 0:
       x = x - 1
       if x == 3:
           continue
       print x,

4 2 1 0
					
						


Last updated on 1/30/2002
Python Developer's Handbook, © 2002 Sams Publishing

< BACKMake Note | BookmarkCONTINUE >

Index terms contained in this section

control statements 2nd
else statement 2nd
if/elif/else statement
pass statement
statements
      control 2nd
      else 2nd
      if/elif/else
      pass
      while
syntax
     statements
            for
            if/elif/else
while statement

2002, O'Reilly & Associates, Inc.

...
Expand> <Close

Want complete source code? Download it here

Point(s): 1

Download
0 lines left, continue to read
Sponsored links

File list

Tips: You can preview the content of files by clicking file names^_^
Name Size Date
0672319942.html3.37 kB01-06-02 20:06
1.html5.10 kB01-06-02 20:06
10.html3.69 kB01-06-02 20:06
100.html5.41 kB01-06-02 20:06
101.html7.96 kB01-06-02 20:06
102.html3.75 kB01-06-02 20:06
103.html3.75 kB01-06-02 20:06
104.html5.81 kB01-06-02 20:06
105.html16.46 kB01-06-02 20:06
106.html25.87 kB01-06-02 20:06
107.html7.44 kB01-06-02 20:06
108.html20.95 kB01-06-02 20:06
109.html10.02 kB01-06-02 20:06
11.html3.66 kB01-06-02 20:06
110.html9.58 kB01-06-02 20:06
111.html9.96 kB01-06-02 20:06
112.html11.34 kB01-06-02 20:06
113.html7.87 kB01-06-02 20:06
114.html13.56 kB01-06-02 20:06
115.html3.76 kB01-06-02 20:06
116.html3.76 kB01-06-02 20:06
117.html4.27 kB01-06-02 20:06
118.html4.27 kB01-06-02 20:06
119.html9.45 kB01-06-02 20:06
12.html3.66 kB01-06-02 20:06
120.html8.62 kB01-06-02 20:06
121.html65.99 kB01-06-02 20:06
122.html28.42 kB01-06-02 20:06
123.html14.92 kB01-06-02 20:06
124.html7.17 kB01-06-02 20:06
125.html24.21 kB01-06-02 20:06
126.html10.82 kB01-06-02 20:06
127.html10.54 kB01-06-02 20:06
128.html3.86 kB01-06-02 20:06
129.html3.86 kB01-06-02 20:06
13.html12.82 kB01-06-02 20:06
130.html5.85 kB01-06-02 20:06
131.html5.30 kB01-06-02 20:06
132.html29.95 kB01-06-02 20:06
133.html61.54 kB01-06-02 20:06
134.html40.34 kB01-06-02 20:06
135.html9.11 kB01-06-02 20:06
136.html15.53 kB01-06-02 20:06
137.html3.86 kB01-06-02 20:06
138.html3.86 kB01-06-02 20:06
139.html5.80 kB01-06-02 20:06
14.html11.79 kB01-06-02 20:06
140.html14.32 kB01-06-02 20:06
141.html26.46 kB01-06-02 20:06
142.html21.93 kB01-06-02 20:06
143.html17.03 kB01-06-02 20:06
144.html7.95 kB01-06-02 20:06
145.html28.59 kB01-06-02 20:06
146.html52.14 kB01-06-02 20:06
147.html8.37 kB01-06-02 20:06
148.html3.63 kB01-06-02 20:06
149.html3.63 kB01-06-02 20:06
15.html10.93 kB01-06-02 20:06
150.html4.42 kB01-06-02 20:06
151.html16.23 kB01-06-02 20:06
152.html32.55 kB01-06-02 20:06
153.html13.13 kB01-06-02 20:06
154.html28.33 kB01-06-02 20:06
155.html40.15 kB01-06-02 20:06
156.html23.47 kB01-06-02 20:06
157.html7.73 kB01-06-02 20:06
158.html10.61 kB01-06-02 20:06
159.html3.72 kB01-06-02 20:06
16.html11.42 kB01-06-02 20:06
160.html3.72 kB01-06-02 20:06
161.html3.64 kB01-06-02 20:06
162.html3.64 kB01-06-02 20:06
163.html4.70 kB01-06-02 20:06
164.html60.18 kB01-06-02 20:06
165.html42.25 kB01-06-02 20:06
166.html17.91 kB01-06-02 20:06
167.html9.76 kB01-06-02 20:06
168.html13.52 kB01-06-02 20:06
169.html10.35 kB01-06-02 20:06
17.html17.40 kB01-06-02 20:06
170.html9.08 kB01-06-02 20:06
171.html3.61 kB01-06-02 20:06
172.html3.61 kB01-06-02 20:06
173.html6.95 kB01-06-02 20:06
174.html27.86 kB01-06-02 20:06
175.html28.55 kB01-06-02 20:06
176.html16.39 kB01-06-02 20:06
177.html24.60 kB01-06-02 20:06
178.html10.20 kB01-06-02 20:06
179.html3.62 kB01-06-02 20:06
18.html12.04 kB01-06-02 20:06
180.html3.62 kB01-06-02 20:06
181.html7.21 kB01-06-02 20:06
182.html11.83 kB01-06-02 20:06
183.html17.37 kB01-06-02 20:06
184.html87.57 kB01-06-02 20:06
185.html25.23 kB01-06-02 20:06
186.html6.62 kB01-06-02 20:06
187.html3.73 kB01-06-02 20:06
188.html3.73 kB01-06-02 20:06
189.html4.76 kB01-06-02 20:06
19.html5.49 kB01-06-02 20:06
190.html74.34 kB01-06-02 20:06
191.html9.56 kB01-06-02 20:06
192.html31.86 kB01-06-02 20:06
193.html67.73 kB01-06-02 20:06
194.html69.48 kB01-06-02 20:06
195.html32.75 kB01-06-02 20:06
196.html10.74 kB01-06-02 20:06
197.html3.54 kB01-06-02 20:06
198.html3.54 kB01-06-02 20:06
199.html3.81 kB01-06-02 20:06
2.html5.10 kB01-06-02 20:06
20.html9.25 kB01-06-02 20:06
200.html3.81 kB01-06-02 20:06
201.html8.82 kB01-06-02 20:06
202.html7.07 kB01-06-02 20:06
203.html50.32 kB01-06-02 20:06
204.html8.07 kB01-06-02 20:06
205.html7.53 kB01-06-02 20:06
206.html3.60 kB01-06-02 20:06
207.html3.60 kB01-06-02 20:06
208.html7.22 kB01-06-02 20:06
209.html21.63 kB01-06-02 20:06
21.html5.84 kB01-06-02 20:06
210.html24.67 kB01-06-02 20:06
211.html30.17 kB01-06-02 20:06
212.html159.15 kB01-06-02 20:06
213.html18.72 kB01-06-02 20:06
214.html6.54 kB01-06-02 20:06
215.html7.22 kB01-06-02 20:06
216.html6.76 kB01-06-02 20:06
217.html3.11 kB01-06-02 20:06
218.html3.54 kB01-06-02 20:06
219.html4.14 kB01-06-02 20:06
22.html3.69 kB01-06-02 20:06
220.html4.14 kB01-06-02 20:06
221.html4.82 kB01-06-02 20:06
222.html50.92 kB01-06-02 20:06
223.html3.87 kB01-06-02 20:06
224.html57.67 kB01-06-02 20:06
225.html37.66 kB01-06-02 20:06
226.html5.04 kB01-06-02 20:06
227.html3.85 kB01-06-02 20:06
228.html3.85 kB01-06-02 20:06
229.html4.47 kB01-06-02 20:06
23.html3.69 kB01-06-02 20:06
230.html21.41 kB01-06-02 20:06
231.html19.56 kB01-06-02 20:06
232.html26.27 kB01-06-02 20:06
233.html10.07 kB01-06-02 20:06
234.html22.22 kB01-06-02 20:06
235.html36.83 kB01-06-02 20:06
236.html49.23 kB01-06-02 20:06
237.html16.63 kB01-06-02 20:06
238.html6.96 kB01-06-02 20:06
239.html3.09 kB01-06-02 20:06
24.html4.86 kB01-06-02 20:06
240.html3.43 kB01-06-02 20:06
241.html3.59 kB01-06-02 20:06
242.html3.59 kB01-06-02 20:06
243.html17.49 kB01-06-02 20:06
244.html9.38 kB01-06-02 20:06
245.html16.62 kB01-06-02 20:06
246.html9.81 kB01-06-02 20:06
247.html11.50 kB01-06-02 20:06
248.html8.95 kB01-06-02 20:06
249.html8.93 kB01-06-02 20:06
25.html11.48 kB01-06-02 20:06
250.html10.89 kB01-06-02 20:06
251.html8.21 kB01-06-02 20:06
252.html5.14 kB01-06-02 20:06
253.html3.61 kB01-06-02 20:06
254.html3.61 kB01-06-02 20:06
255.html4.61 kB01-06-02 20:06
256.html4.61 kB01-06-02 20:06
257.html43.07 kB01-06-02 20:06
258.html10.12 kB01-06-02 20:06
259.html7.99 kB01-06-02 20:06
26.html25.88 kB01-06-02 20:06
260.html17.17 kB01-06-02 20:06
261.html10.99 kB01-06-02 20:06
262.html15.70 kB01-06-02 20:06
263.html36.19 kB01-06-02 20:06
264.html61.93 kB01-06-02 20:06
265.html39.81 kB01-06-02 20:06
266.html15.13 kB01-06-02 20:06
267.html16.34 kB01-06-02 20:06
268.html3.55 kB01-06-02 20:06
269.html3.55 kB01-06-02 20:06
27.html27.92 kB01-06-02 20:06
270.html14.30 kB01-06-02 20:06
271.html14.21 kB01-06-02 20:06
272.html9.44 kB01-06-02 20:06
273.html8.41 kB01-06-02 20:06
274.html5.45 kB01-06-02 20:06
275.html5.45 kB01-06-02 20:06
276.html8.08 kB01-06-02 20:06
277.html9.78 kB01-06-02 20:06
278.html6.04 kB01-06-02 20:06
279.html6.89 kB01-06-02 20:06
28.html12.02 kB01-06-02 20:06
280.html11.77 kB01-06-02 20:06
281.html10.18 kB01-06-02 20:06
282.html4.98 kB01-06-02 20:06
283.html4.98 kB01-06-02 20:06
284.html4.12 kB01-06-02 20:06
285.html5.78 kB01-06-02 20:06
286.html12.42 kB01-06-02 20:06
287.html6.87 kB01-06-02 20:06
29.html45.69 kB01-06-02 20:06
3.html5.51 kB01-06-02 20:06
30.html10.03 kB01-06-02 20:06
31.html23.06 kB01-06-02 20:06
32.html22.26 kB01-06-02 20:06
33.html18.88 kB01-06-02 20:06
34.html18.25 kB01-06-02 20:06
35.html15.70 kB01-06-02 20:06
36.html5.50 kB01-06-02 20:06
37.html11.83 kB01-06-02 20:06
38.html3.69 kB01-06-02 20:06
39.html3.69 kB01-06-02 20:06
4.html5.51 kB01-06-02 20:06
40.html8.24 kB01-06-02 20:06
41.html12.92 kB01-06-02 20:06
42.html4.51 kB01-06-02 20:06
43.html3.90 kB01-06-02 20:06
44.html3.52 kB01-06-02 20:06
45.html5.99 kB01-06-02 20:06
46.html4.33 kB01-06-02 20:06
47.html4.19 kB01-06-02 20:06
48.html4.01 kB01-06-02 20:06
49.html3.95 kB01-06-02 20:06
5.html4.69 kB01-06-02 20:06
50.html3.63 kB01-06-02 20:06
51.html3.75 kB01-06-02 20:06
52.html5.56 kB01-06-02 20:06
53.html4.41 kB01-06-02 20:06
54.html6.99 kB01-06-02 20:06
55.html3.52 kB01-06-02 20:06
56.html3.95 kB01-06-02 20:06
57.html3.69 kB01-06-02 20:06
58.html4.27 kB01-06-02 20:06
59.html3.88 kB01-06-02 20:06
6.html4.69 kB01-06-02 20:06
60.html3.58 kB01-06-02 20:06
61.html4.17 kB01-06-02 20:06
62.html3.93 kB01-06-02 20:06
63.html3.68 kB01-06-02 20:06
64.html4.16 kB01-06-02 20:06
65.html4.04 kB01-06-02 20:06
66.html4.97 kB01-06-02 20:06
67.html3.91 kB01-06-02 20:06
68.html3.55 kB01-06-02 20:06
69.html3.51 kB01-06-02 20:06
7.html10.67 kB01-06-02 20:06
70.html3.52 kB01-06-02 20:06
71.html3.83 kB01-06-02 20:06
72.html4.02 kB01-06-02 20:06
73.html21.61 kB01-06-02 20:06
74.html12.94 kB01-06-02 20:06
75.html31.26 kB01-06-02 20:06
76.html11.98 kB01-06-02 20:06
77.html4.24 kB01-06-02 20:06
78.html4.26 kB01-06-02 20:06
79.html10.95 kB01-06-02 20:06
8.html10.67 kB01-06-02 20:06
80.html12.11 kB01-06-02 20:06
81.html4.88 kB01-06-02 20:06
82.html6.48 kB01-06-02 20:06
83.html5.64 kB01-06-02 20:06
84.html13.30 kB01-06-02 20:06
85.html7.00 kB01-06-02 20:06
86.html3.90 kB01-06-02 20:06
87.html4.59 kB01-06-02 20:06
88.html5.00 kB01-06-02 20:06
89.html17.71 kB01-06-02 20:06
9.html3.69 kB01-06-02 20:06
90.html6.00 kB01-06-02 20:06
91.html3.68 kB01-06-02 20:06
92.html3.68 kB01-06-02 20:06
93.html12.98 kB01-06-02 20:06
94.html10.60 kB01-06-02 20:06
95.html19.93 kB01-06-02 20:06
96.html10.34 kB01-06-02 20:06
97.html6.27 kB01-06-02 20:06
98.html6.77 kB01-06-02 20:06
99.html16.97 kB01-06-02 20:06
front_matter.html4.16 kB01-06-02 20:06
index.html3.37 kB01-06-02 20:06
new_toc.html15.79 kB01-06-02 20:06
rindex1.html53.02 kB01-06-02 20:05
rindex10.html5.16 kB01-06-02 20:05
rindex11.html3.96 kB01-06-02 20:05
rindex12.html15.07 kB01-06-02 20:05
rindex13.html84.43 kB01-06-02 20:05
rindex14.html10.85 kB01-06-02 20:05
rindex15.html26.04 kB01-06-02 20:05
rindex16.html58.33 kB01-06-02 20:05
rindex17.html3.52 kB01-06-02 20:05
rindex18.html16.83 kB01-06-02 20:05
rindex19.html52.89 kB01-06-02 20:05
rindex2.html13.47 kB01-06-02 20:05
rindex20.html17.55 kB01-06-02 20:05
rindex21.html13.56 kB01-06-02 20:05
rindex22.html10.63 kB01-06-02 20:05
rindex23.html16.92 kB01-06-02 20:05
rindex24.html4.90 kB01-06-02 20:05
rindex25.html2.50 kB01-06-02 20:05
rindex3.html43.59 kB01-06-02 20:06
rindex4.html21.76 kB01-06-02 20:06
rindex5.html22.31 kB01-06-02 20:06
rindex6.html36.57 kB01-06-02 20:06
rindex7.html14.06 kB01-06-02 20:06
rindex8.html11.93 kB01-06-02 20:06
rindex9.html25.33 kB01-06-02 20:06
toc.html24.97 kB01-06-02 20:06
<(ebook>0.00 BPython) O'Reilly
<0672319942>0.00 B25-08-02 17:24
<graphics>0.00 B25-08-02 17:24
<images>0.00 B25-08-02 17:24
<oreillyi>0.00 B25-08-02 17:24
oreillyM.css4.42 kB31-05-02 17:16
oreillyN.css4.42 kB31-05-02 17:16
00.gif41.00 B31-05-02 17:16
01fig01.gif58.03 kB28-01-02 08:54
01fig02.gif39.76 kB28-01-02 08:54
01fig03.gif22.06 kB28-01-02 08:54
01fig04.gif64.75 kB28-01-02 08:54
02fig01.gif54.48 kB28-01-02 08:54
02fig02.gif16.29 kB28-01-02 08:54
02fig03.gif14.11 kB28-01-02 08:54
02fig04.gif47.82 kB28-01-02 08:54
06fig01.gif32.19 kB28-01-02 08:54
06fig02.gif58.39 kB28-01-02 08:54
06fig03.gif48.96 kB28-01-02 08:54
07fig01.gif47.96 kB28-01-02 08:54
07fig02.gif8.99 kB28-01-02 08:54
07fig03.gif9.46 kB28-01-02 08:54
07fig04.gif11.51 kB28-01-02 08:54
07fig05.gif8.27 kB28-01-02 08:54
07fig06.gif31.46 kB28-01-02 08:54
12fig01.gif34.54 kB28-01-02 08:54
15fig01.gif1.30 kB28-01-02 08:54
15fig02.gif1.50 kB28-01-02 08:54
15fig03.gif5.93 kB28-01-02 08:54
15fig04.gif924.00 B28-01-02 08:54
15fig05.gif1.55 kB28-01-02 08:54
15fig06.gif1.62 kB28-01-02 08:54
15fig07.gif1.69 kB28-01-02 08:54
15fig08.gif1.02 kB28-01-02 08:54
15fig09.gif2.54 kB28-01-02 08:54
15fig10.gif1.92 kB28-01-02 08:54
15fig11.gif2.44 kB28-01-02 08:54
15fig12.gif2.48 kB28-01-02 08:54
15fig13.gif2.36 kB28-01-02 08:54
15fig14.gif5.43 kB28-01-02 08:54
15fig15.gif5.51 kB28-01-02 08:54
15fig16.gif2.18 kB28-01-02 08:54
15fig17.gif12.22 kB28-01-02 08:54
16fig01.gif28.99 kB28-01-02 08:54
16fig02.gif23.02 kB28-01-02 08:54
16fig03.gif32.48 kB28-01-02 08:54
16fig04.gif17.27 kB28-01-02 08:54
16fig05.gif23.88 kB28-01-02 08:54
16fig06.gif23.85 kB28-01-02 08:54
16fig07.gif36.76 kB28-01-02 08:54
16fig08.gif20.66 kB28-01-02 08:54
16fig09.gif71.63 kB28-01-02 08:54
16fig10.gif23.23 kB28-01-02 08:54
16fig11.gif22.97 kB28-01-02 08:54
16fig12.gif22.06 kB28-01-02 08:54
16fig13.gif49.73 kB28-01-02 08:54
16fig14.gif60.34 kB28-01-02 08:54
18fig01.gif63.94 kB28-01-02 08:54
18fig02.gif24.07 kB28-01-02 08:54
ccc.gif109.00 B28-01-02 08:54
spacer.gif41.00 B31-05-02 17:16
view.gif41.00 B31-05-02 17:16
0672319942_s.jpg2.91 kB29-01-02 11:29
...
Sponsored links
  • Sent successfully!
  • 1 point

30.html (1.65 MB)

Need 1 point
Your Point(s)

Your Point isn't enough.

Get point immediately by PayPal

More(Debit card / Credit card / PayPal Credit / Online Banking)

Submit your source codes. Get more point

LOGIN

Don't have an account? Register now
Need any help?
Mail to: support@codeforge.com

切换到中文版?

Where are you going?

^_^"Oops ...

Sorry!This guy is mysterious, its blog hasn't been opened, try another, please!
OK

Warm tip!

CodeForge to FavoriteFavorite by Ctrl+D