blocks|key|160117|text|要首先回答一般问题，通常需要在编写代码时使用打印功能将脚本中的信息输出到屏幕上，以确保得到预期的结果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|160118|随着代码变得越来越复杂，您可能会发现日志记录比打印更好，但这是另一个答案。|160119|在与Python解释器的交互会话中回显的打印和返回值的表示之间有很大的不同。打印应打印到您的标准输出。在脚本中运行等价代码时，表达式返回值的回显表示(如果不是None，则显示在Python+shell中)将保持静默。|offset|length|style|CODE|160120|1.打印|160121|在Python+2中，我们有print语句。在Python+3中，我们得到了一个print函数，我们也可以在Python+2中使用它。|160122|使用逗号打印语句(Python+2)|160123|使用逗号分隔项目的print语句使用空格分隔项目。后面的逗号将导致附加另一个空格。末尾逗号不会附加要附加到打印项目的换行符。|160124|您可以将每一项放在单独的print语句中，并在每一项之后使用逗号，它们将在同一行上打印相同的内容。|160125|例如(这只能在脚本中工作，在交互式shell中，每行后面都会有一个新的提示)：|160126|x+=+"Hello"
y+=+"World"

print+"I+am+printing",
print+x,
print+y+|code-block|syntax|javascript|160127|将输出：|160128|I+am+printing+Hello+World|160129|打印功能|160130|使用Python+3的内置打印功能，Python+2.6和2.7中也提供了此导入功能：|160131|from+__future__+import+print_function|160132|你可以声明一个分隔符和一个结束，这给了我们更多的灵活性：|160133|>>>+print('hello',+'world',+sep='-',+end='\n****\n')
hello-world
****
>>>|160134|sep的默认值为'+'，end的默认值为'\n'：|160135|>>>+print('hello',+'world')
hello+world
>>>+|160136|2.字符串拼接|160137|连接在内存中创建每个字符串，然后在它们的末端将它们组合在一个新的字符串中(因此这可能不是非常适合内存)，然后同时将它们打印到您的输出。当您需要将字符串连接在一起时，这是很好的。|160138|print('hello'+%2B+'-'+%2B+'world')|160139|将打印|160140|hello-world|160141|在尝试以这种方式将其他类型的文字连接到字符串之前要小心，要先将文字转换为字符串。|160142|print('here+is+a+number:+'+%2B+str(2))|160143|打印|160144|here+is+a+number:+2|160145|如果您尝试连接整数而不先将其强制转换为字符串：|160146|>>>+print('here+is+a+number:+'+%2B+2)
Traceback+(most+recent+call+last):
++File+"<stdin>",+line+1,+in+<module>
TypeError:+cannot+concatenate+'str'+and+'int'+objects|160147|这应该说明，您应该只尝试连接已知为字符串的变量。接下来演示的新格式化方法将为您处理此问题。|160148|3.字符串插值|160149|您正在演示的格式是借鉴自C的旧样式的字符串插值。它采用旧的字符串，然后一次创建新的字符串。它的作用相当简单。当您可能要构建一个相当大的模板时(在3%2B行和3%2B变量中，您肯定应该这样做)，您应该使用它。|160150|这样做的新方法是(使用参数的索引)：|160151|print('I+am+printing+{0}+and+{1}'.format(x,+y))|160152|或者在python+2.7或3中(使用隐含索引)：|160153|print('I+am+printing+{}+and+{}'.format(x,+y))|160154|或者使用命名参数(这在语义上很容易读懂，但代码看起来不是很枯燥(即不要重复))|160155|print('I+am+printing+{x}+and+{y}'.format(x=x,+y=y))|160156|与%25样式格式化(这里没有演示)相比，它的最大好处是允许您组合位置参数和关键字参数|160157|print('I+am+printing+{0}+and+{y}'.format(x,+y=y))|160158|Python+3.6中的新功能，格式化文字|160159|Python3.6将拥有format+literals，具有更优雅的语法(冗余更少)。简单的语法类似于：|160160|print(f'I+am+printing+{x}+and+{y}')|160161|格式文字实际上可以就地执行代码：|160162|>>>+print(f'I+am+printing+{"hello".capitalize()}+and+{"Wo"+%2B+"rld"}')
I+am+printing+Hello+and+World|160163|entityMap|0|LINK|mutability|MUTABLE|url|https://www.python.org/dev/peps/pep-0498/^0|0|0|27|4|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|8|3|K|4|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1|1|0|0|0|C|F|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|38|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|39|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|3A|8|@$F|3B|G|3C|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|3D|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|3E|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|3F|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|3G|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|3H|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|3I|8|@]|9|@]|A|$]]|$1|V|3|W|5|X|7|3J|8|@]|9|@]|A|$Y|Z]]|$1|10|3|11|5|6|7|3K|8|@]|9|@]|A|$]]|$1|12|3|13|5|X|7|3L|8|@]|9|@]|A|$Y|Z]]|$1|14|3|15|5|6|7|3M|8|@]|9|@]|A|$]]|$1|16|3|17|5|6|7|3N|8|@]|9|@]|A|$]]|$1|18|3|19|5|X|7|3O|8|@]|9|@]|A|$Y|Z]]|$1|1A|3|1B|5|6|7|3P|8|@]|9|@]|A|$]]|$1|1C|3|1D|5|X|7|3Q|8|@]|9|@]|A|$Y|Z]]|$1|1E|3|1F|5|6|7|3R|8|@$F|3S|G|3T|H|I]|$F|3U|G|3V|H|I]]|9|@]|A|$]]|$1|1G|3|1H|5|X|7|3W|8|@]|9|@]|A|$Y|Z]]|$1|1I|3|1J|5|6|7|3X|8|@]|9|@]|A|$]]|$1|1K|3|1L|5|6|7|3Y|8|@]|9|@]|A|$]]|$1|1M|3|1N|5|X|7|3Z|8|@]|9|@]|A|$Y|Z]]|$1|1O|3|1P|5|6|7|40|8|@]|9|@]|A|$]]|$1|1Q|3|1R|5|X|7|41|8|@]|9|@]|A|$Y|Z]]|$1|1S|3|1T|5|6|7|42|8|@]|9|@]|A|$]]|$1|1U|3|1V|5|X|7|43|8|@]|9|@]|A|$Y|Z]]|$1|1W|3|1X|5|6|7|44|8|@]|9|@]|A|$]]|$1|1Y|3|1Z|5|X|7|45|8|@]|9|@]|A|$Y|Z]]|$1|20|3|21|5|6|7|46|8|@]|9|@]|A|$]]|$1|22|3|23|5|X|7|47|8|@]|9|@]|A|$Y|Z]]|$1|24|3|25|5|6|7|48|8|@]|9|@]|A|$]]|$1|26|3|27|5|6|7|49|8|@]|9|@]|A|$]]|$1|28|3|29|5|6|7|4A|8|@]|9|@]|A|$]]|$1|2A|3|2B|5|6|7|4B|8|@]|9|@]|A|$]]|$1|2C|3|2D|5|X|7|4C|8|@]|9|@]|A|$Y|Z]]|$1|2E|3|2F|5|6|7|4D|8|@]|9|@]|A|$]]|$1|2G|3|2H|5|X|7|4E|8|@]|9|@]|A|$Y|Z]]|$1|2I|3|2J|5|6|7|4F|8|@]|9|@]|A|$]]|$1|2K|3|2L|5|X|7|4G|8|@]|9|@]|A|$Y|Z]]|$1|2M|3|2N|5|6|7|4H|8|@$F|4I|G|4J|H|I]]|9|@]|A|$]]|$1|2O|3|2P|5|X|7|4K|8|@]|9|@]|A|$Y|Z]]|$1|2Q|3|2R|5|6|7|4L|8|@]|9|@]|A|$]]|$1|2S|3|2T|5|6|7|4M|8|@]|9|@$F|4N|G|4O|1|4P]]|A|$]]|$1|2U|3|2V|5|X|7|4Q|8|@]|9|@]|A|$Y|Z]]|$1|2W|3|2X|5|6|7|4R|8|@]|9|@]|A|$]]|$1|2Y|3|2Z|5|X|7|4S|8|@]|9|@]|A|$Y|Z]]|$1|30|3|-4|5|6|7|4T|8|@]|9|@]|A|$]]]|31|$32|$5|33|34|35|A|$36|37]]]]

To answer the general question first, you would use printing in general to output information in your scripts to the screen when you're writing code to ensure that you're getting what you expect. 

As your code becomes more sophisticated, you may find that logging would be better than printing, but that's information for another answer.

There is a big difference between printing and the return values' representations that are echoed in an interactive session with the Python interpreter. Printing should print to your standard output. The echoed representation of the expression's return value (that show up in your Python shell if not <code>None</code>) will be silent when running the equivalent code in scripts.

<h1>1. Printing</h1>

In Python 2, we had print statements. In Python 3, we get a print function, which we can also use in Python 2.

<h2>Print Statements with Commas (Python 2)</h2>

The print statement with commas separating items, uses a space to separate them. A trailing comma will cause another space to be appended. No trailing comma will append a newline character to be appended to your printed item.

You could put each item on a separate print statement and use a comma after each and they would print the same, on the same line.

For example (this would only work in a script, in an interactive shell, you'd get a new prompt after every line):

<pre><code>x = "Hello"
y = "World"

print "I am printing",
print x,
print y 
</code></pre>

Would output:

<pre><code>I am printing Hello World
</code></pre>

<h2>Print Function</h2>

With the built-in print function from Python 3, also available in Python 2.6 and 2.7 with this import:

<pre><code>from __future__ import print_function
</code></pre>

you can declare a separator and an end, which gives us a lot more flexibility:

<pre><code>&gt;&gt;&gt; print('hello', 'world', sep='-', end='\n****\n')
hello-world
****
&gt;&gt;&gt;
</code></pre>

The defaults are <code>' '</code> for sep and <code>'\n'</code> for end:

<pre><code>&gt;&gt;&gt; print('hello', 'world')
hello world
&gt;&gt;&gt; 
</code></pre>

<h1>2. String Concatenation</h1>

Concatenation creates each string in memory, and then combines them together at their ends in a new string (so this may not be very memory friendly), and then prints them to your output at the same time. This is good when you need to join strings, likely constructed elsewhere, together. 

<pre><code>print('hello' + '-' + 'world')
</code></pre>

will print

<pre><code>hello-world
</code></pre>

Be careful before you attempt to join in this manner literals of other types to strings, to convert the literals to strings first. 

<pre><code>print('here is a number: ' + str(2))
</code></pre>

prints

<pre><code>here is a number: 2
</code></pre>

If you attempt to concatenate the integer without coercing it to a string first:

<pre><code>&gt;&gt;&gt; print('here is a number: ' + 2)
Traceback (most recent call last):
 File "&lt;stdin&gt;", line 1, in &lt;module&gt;
TypeError: cannot concatenate 'str' and 'int' objects
</code></pre>

This should demonstrate that you should only ever attempt to concatenate variables that are known to be strings. The new way of formatting demonstrated next handles this issue for you.

<h1>3. String Interpolation</h1>

The formatting you're demonstrating is the old style of string interpolation, borrowed from C. It takes the old string and one time creates a new one. What it does is fairly straightforward. You should use this when you may seem likely to building up a fairly large template (at 3+ lines and 3+ variables, you definitely should be doing it this way).

The new way of doing that would be to do this (using the index of the arguments):

<pre><code>print('I am printing {0} and {1}'.format(x, y))
</code></pre>

or in python 2.7 or 3 (using the implied index):

<pre><code>print('I am printing {} and {}'.format(x, y))
</code></pre>

or with named arguments (this is semantically easy to read, but the code doesn't look very DRY (i.e. Don't Repeat Yourself))

<pre><code>print('I am printing {x} and {y}'.format(x=x, y=y))
</code></pre>

The biggest benefit of this over <code>%</code> style formatting (not demonstrated here) is that it lets you combine positional and keyword arguments

<pre><code>print('I am printing {0} and {y}'.format(x, y=y))
</code></pre>

<h2>New in Python 3.6, format literals</h2>

Python 3.6 will have <a href="https://www.python.org/dev/peps/pep-0498/" rel="noreferrer">format literals</a>, with a more elegant syntax (less redundancy). The simple syntax is something like:

<pre><code>print(f'I am printing {x} and {y}')
</code></pre>

The format literals can actually execute code in-place:

<pre><code>&gt;&gt;&gt; print(f'I am printing {"hello".capitalize()} and {"Wo" + "rld"}')
I am printing Hello and World
</code></pre>

blocks|key|4666389|text|您应该构建列表并使用带有分隔符的连接，例如"，".join(list_name)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4666390|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

you should build list and use join with delimiter 
for example 
",".join(list_name)

I am learning python(2.7) on my own.
I have learned that we can use the following ways to put strings and variables together in printing:

<pre><code>x = "Hello"
y = "World"
</code></pre>

By using commas:

<pre><code>print "I am printing" , x, y # I know that using comma gives automatic space
</code></pre>

By using concatenation :

<pre><code>print "I am printing" + " " + x + " " + y 
</code></pre>

By using string formatters

<pre><code>print "I am printing %s %s" % (x, y) 
</code></pre>

In this case all three print the same: 

<pre><code>I am printing Hello World
</code></pre>

What is the difference between the three and are there any particular instances where one is preferred over the other?

Difference between using commas, concatenation, and string formatters in Python

解释器

Python

我正在自学python(2.7)。我了解到，我们可以使用以下方法在打印时将字符串和变量放在一起：x = "Hello"y = "World"使用逗号：print "I am printing" , x, y  # I know that using comma gives automatic space通过使用连接：p...

问在Python中使用逗号、连接和字符串格式化程序的区别
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Python中使用逗号、连接和字符串格式化程序的区别EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Python中使用逗号、连接和字符串格式化程序的区别
EN