序列是Python中的重要数据结构,序列包括字符串,列表,元组。
大部分朋友学习Python的时候都会找本书或者资料从头看到尾,这次我们换一个思路,问答式的方式,可能让我们精力更集中,下面开始我们的提问:
1.什么是序列?
序列是将元素按照顺序排列,通过索引(下标)访问;
2.能直观描述下吗?
直接上图:
image序列中的每个元素按顺序排列,使用索引进行访问,索引分为正负索引;
3.具体如何访问,正负索引是不是有点多余?
举一个栗子,字符串:msg ='helloworld',在jupyter下操作如下:
<pre class="prettyprint hljs bash" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
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获取第一个元素
print(msg[0])
获取最后一个?
print(msg[-1])
获取第3个元素
print(msg[2])
获取第12个元素
print(msg[11])</pre>
输出结果:
<pre class="prettyprint hljs sql" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">h d l
IndexError Traceback (most recent call last)
<ipython-input-6-589026671881> in <module>()
7 print(msg[2])
8 #获取第12个元素
----> 9 print(msg[11])
IndexError: string index out of range</pre>
诶呀我去,怎么出了这么个玩意?一般大家看到这种错误,莫名的头疼,这时候我们会问:
4.访问第一个元素索引为什么是0?
序列的索引从0开始,所以我们访问第一个元素对应索引为0,那么我们访问第二个索引就是2-1,访问第N个元素,索引就是N-1;
5.为什么会出错,这是什么情况?
访问索引超过了序列长度就会报错,因为访问的元素不存在。
6.怎么看这个错误?
Python中出错后,会将出错行,出错信息提示出来,给了我们足够信息去解决问题,具体意思如下:
image下次看到这种错误就查下序列长度与索引值。
7.我想遍历整个序列,难道要msg[1],msg[2]...msg[n]么?
如果你想,这种方式也是可以的;
但是我们一般使用for循环,代码如下:
<pre class="prettyprint hljs fsharp" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">print(msg)
for 遍历序列,依次去msg中的每个元素,
并赋值给val
for val in msg:
print(val)</pre>
8.for循环为什么不会出错?
for 循环内部做了异常处理,所以不会出错,我们直接使用就可以。
9.切片操作是怎么回事?
切片是Python中的操作符,类似函数操作,使用方式如下:
sequence[start:stop]:start为起始索引,stop为结束索引,
结果为:获取索引start到stop-1元素,返回新的序列;
start默认为0,stop默认到最后;
sequence[start:stop:step]:与上类似,step为步进值,默认为1;
10.如何使用切片操作?
举个例子,msg = 'hellowolrd',jupyter下操作如下:
<pre class="prettyprint hljs bash" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
索引从0开始算
获取索引2到4之间元素?
print(msg[2:5]) #stop -1
获取索引0到7之间元素?
print(msg[0:8])
获取索引5之后所有元素?
print(msg[5:11]) #stop -1
print(msg[5:]) #默认到最后
print(msg[5:100])#会不会报错,为什么?</pre>
输出结果:
<pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">llo
hellowor
world
world
world</pre>
11.切片操作有高级使用方式么?
没有高不高级,看如何使用;
同样一块面,你做成馒头他就2元,你做成蛋糕他就有一万种可能。
理解知识点:序列有两种索引:正索引,负索引;
先提出问题,然后自己尝试去实现,可以把答案写在品论区,再继续阅读:
1>索引倒数第3个之后所有元素,
2>索引从0到结束,隔一个取一个,
3>索引倒数第二个开始,向前隔一个取一个元素,
4>切片操作实现倒序,
到这里,应该在自己环境下尝试练习了,我这边继续,具体实现如下:
<pre class="prettyprint hljs bash" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
获取索引倒数第二个元素之后所有元素
print(msg[-2:])
获取索引从0到结束,隔一个取一个元素
理解为,start为0,stop到最后,step为2的切片操作
print(msg[::2])
倒数第二个开始,向前隔一个取一个元素
理解为:start为-2,stop到最前,step为-2的切片操作
print(msg[-2::-2])
切片操作实现倒序?
print(msg[::-1])</pre>
输出结果:
<pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">ld
hlool
loolh
dlrowolleh</pre>
这些搞定了,我们就基本掌握切片操作了。
12.序列支持运算符吗?
运算符 | 是否支持 |
---|---|
算数运算符 | 支持加法与乘法操作,返回新的序列 |
比较运算符 | 支持,返回True与False |
逻辑运算符 | 支持 |
注意:必须是同种类型数据结构操作才有意义。
13.我想要拼接字符串,如何操作?
直接使用加法操作,如下:
<pre class="hljs lua" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">wd1 = 'hello'
wd2 = 'world'
print(wd1 + wd2)
print(wd1 * 2)</pre>
输出结果:
<pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">helloworld
hellohello</pre>
14.取序列长度?
使用len方法:
<pre class="hljs go" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
print(len(msg))</pre>
输出结果:10
15.能否通过索引遍历序列?
能,使用range方法,生成索引,然后使用for循环遍历:
<pre class="prettyprint hljs vim" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
获取长度,生成range对象
使用for遍历range获取索引
通过索引访问元素
for index in range(len(msg)):
print(msg[index])</pre>
16.能否再遍历的时候获取索引与元素?
需要使用enumerate:enumerate(iterable[, start])
参数:iterable:可迭代对象,start:可选参数,指定起始位置;
返回:索引与value对应的enumerate对象;
可以使用for循环进行遍历,具体使用如下:
<pre class="prettyprint hljs bash" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
创建enumerate对象
items = enumerate(msg)
遍历enumerate对象
for item in items:
print(item)</pre>
输出结果:
<pre class="prettyprint hljs scheme" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">(0, 'h')
(1, 'e')
(2, 'l')
(3, 'l')
(4, 'o')
(5, 'w')
(6, 'o')
(7, 'r')
(8, 'l')
(9, 'd')</pre>
17.还没真正获取索引,这个索引和元素在一起如何处理?
是否还记得多元赋值:x,y = 1,2
第一种方式:
<pre class="prettyprint hljs xquery" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
for item in enumerate(msg):
index, value = item
print(index, value)</pre>
第二种方式:
<pre class="prettyprint hljs lua" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">msg = 'helloworld'
for tindex, tvalue in enumerate(msg):
print(tindex, tvalue)</pre>
第一种容易理解,第二种怎么回事?
for循环迭代的时候,首先从 enumerate取元素,而 enumerate的每个元素都是(index, values),我们这里加了两个变量tindex, tvalue去接受值,相当于多元赋值。
18.判断元素是否存再序列中存在?
使用操作符:in与not in
in:元素是否在序列中,在返回True,否则返回False,例如:'a' in 'abc';
not in:与in相反;
实际操作如下:
<pre class="prettyprint hljs python" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">#加法与乘法:
msg = 'helloworld*'
元素是否在序列中
print('w in msg:', 'w' in msg)
print('a in msg:', 'a' in msg)
print('a not in msg:','a' not in msg)</pre>
输出结果:
<pre class="hljs vbscript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">w in msg: True
a in msg: False
a not in msg: True</pre>
好了,到这里我们对序列基本知识点就有了一定认识。
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