Project Python – Free Interactive Book That Introduces Python Programming and CS

The thing is that "advanced Python" is too large a topic for a single book, or even for a single person to cover completely. It might be a series of books though; off the top of my head I can think of the following topics, each of which will cover many advanced areas:

    - Python concurrency: multiprocessing, multithreading and asynchronous programming
    - data science and numerical computation in Python
    - embedded Python
    - Python GUI development
    - packaging and deployment of Python applications and libraries

There's one "Fluent python" by Luciano Ramalho

Have you seen Higher Order Perl by Mark Jason Dominus?

do you have suggestion on books? i need to progress form beginner to intermedite to adv. Any online class/MOOC?

Ok, this was more complex than I thought. I hope I got it right and this gives you some pointers how I investigated. :)

Use type() to see what you are getting:

    >>> type(df.describe().mean())
    <class 'pandas.core.series.Series'>
    >>> type(df.describe().mean)
    <class 'method'>

Something without parenthesis cannot be a method call, at least not from a normal viewpoint. Instead you are trying to access the attribute "mean" of the result of describe() if you run df.groupby(df.var1).describe().mean. This attribute might very well be a method itself (a method object).

Last in that chain was describe(), so let's look at that: https://pandas.pydata.org/pandas-docs/stable/generated/panda...

It returns a "summary: Series/DataFrame of summary statistics", so calling .mean() on that, will call https://pandas.pydata.org/pandas-docs/stable/generated/panda...

Accessing .mean will instead return that method object itself.

By default pandas will return a string describing the data itself when printing a method:

    >>> df.describe()
           numeric   n2
    count      3.0  3.0
    mean       2.0  3.0
    std        1.0  1.0
    min        1.0  2.0
    25%        1.5  2.5
    50%        2.0  3.0
    75%        2.5  3.5
    max        3.0  4.0
    >>> df.describe().mean
    <bound method DataFrame.mean of        numeric   n2
    count      3.0  3.0
    mean       2.0  3.0
    std        1.0  1.0
    min        1.0  2.0
    25%        1.5  2.5
    50%        2.0  3.0
    75%        2.5  3.5
    max        3.0  4.0>
    >>> df.describe().mean()
    numeric    2.00
    n2         2.75
    dtype: float64

I assume this is what threw you off? You are not using the "results" of .mean in further code but were just looking at them, right?

This is very Pandas specific, but I’m going to give you my intuition with a bit of Python knowledge (10yrs):

1. Anything that doesn’t have parens is either an attribute or a property. A property is basically an attribute, except that a computation of some sort is usually executed to set/get its value, whereas an attribute has its value set explicitly. Look at the source to identify if the result of the first code block sets an attribute named `mean` or if it has an `@property` declaration named `mean`. Either way, they’re roughly the same when using them in code.

2. The fact that both `describe()` method examples can have another function and attribute/property chained to their result means `describe()` is returning an object of some type that is not a stdlib data type.

3. The `df.groupby().describe()` is likely returning a different type of object than the second `df.describe()`, as evidenced by the first result having a `mean` attr/property, while the second has a `mean()` function.

From here, I’d start by inspecting the object type returned by `df.groupby()`, `df.groupby().describe()`, and the `df.describe()` to discover the differences.

The question you're asking is really about the Pandas library and its API, not so much about Python the language as such.

Python objects can have both callable methods (e.g. mean()) and properties/attributes that don't need an explicit call (e.g. mean). For whatever reason, it looks like Pandas' describe() method returns a result with a different interface when called with an argument than without one.

Since there is no license listed, the default is they retain full copyright/all rights reserved.