df.head()和df.head有什么区别? [英] What's the difference between df.head() and df.head?

问题描述

在Jupyter Notebook或终端中，df.head和df.head()都可以返回数据帧的输出，但有一些细微差别.这两个不同表达式之间的根本区别是什么?括号通常在Python中扮演什么角色? 谢谢！

In Jupyter Notebook or terminal, both df.head and df.head() can return an output of the dataframe, with some minor differences. What's the fundamental difference between the two different expressions and what role does parenthesis play in Python in general? Thanks!

>>>df.head
<bound method NDFrame.head of          Date    Open    High     Low   Close    Volume
0    1-Jun-17  153.17  153.33  152.22  153.18  16404088
1    2-Jun-17  153.58  155.45  152.89  155.45  27770715
2    5-Jun-17  154.34  154.45  153.46  153.93  25331662
3    6-Jun-17  153.90  155.81  153.78  154.45  26624926
4    7-Jun-17  155.02  155.98  154.48  155.37  21069647
5    8-Jun-17  155.25  155.54  154.40  154.99  21250798
6    9-Jun-17  155.19  155.19  146.02  148.98  64882657
7   12-Jun-17  145.74  146.09  142.51  145.42  72307330
8   13-Jun-17  147.16  147.45  145.15  146.59  34165445
9   14-Jun-17  147.50  147.50  143.84  145.16  31531232
10  15-Jun-17  143.32  144.48  142.21  144.29  32165373
>>> df.head()
       Date    Open    High     Low   Close    Volume
0  1-Jun-17  153.17  153.33  152.22  153.18  16404088
1  2-Jun-17  153.58  155.45  152.89  155.45  27770715
2  5-Jun-17  154.34  154.45  153.46  153.93  25331662
3  6-Jun-17  153.90  155.81  153.78  154.45  26624926
4  7-Jun-17  155.02  155.98  154.48  155.37  21069647

推荐答案

这些不只是微小差异".实际上，df.head根本使您无法接受.

Those aren't just "minor differences". You didn't actually take the head at all with df.head.

df.head()实际上是数据帧的开头.您可以看到输出只有5行:

df.head() actually takes the head of the dataframe. You can see that the output only has 5 rows:

>>> df.head()
       Date    Open    High     Low   Close    Volume
0  1-Jun-17  153.17  153.33  152.22  153.18  16404088
1  2-Jun-17  153.58  155.45  152.89  155.45  27770715
2  5-Jun-17  154.34  154.45  153.46  153.93  25331662
3  6-Jun-17  153.90  155.81  153.78  154.45  26624926
4  7-Jun-17  155.02  155.98  154.48  155.37  21069647

相反，df.head只是数据帧df的head方法的方法对象.需要括号才能实际调用该方法.方法对象的repr基本上是

In contrast, df.head is just a method object for the head method of the dataframe df. The parentheses are needed to actually call the method. The method object's repr is basically

f"<bound method {classname}.{methodname} of {object!r}"

，在适当的位置替换了对象的类名称，方法名称和repr.实际上，看起来像数据帧的输出部分是原始df的repr.它有10行而不是5行，因为它是整个原始数据帧，而不是头部.

with the class name, method name, and repr of the object substituted in the appropriate places. The part of the output that looks like a dataframe is, in fact, the repr of the original df. It has 10 rows instead of 5 because it's the whole original dataframe, not the head.

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