Praktik terbaik untuk argumen default

Salah satu rekan kerja Anda (yang jelas belum mengambil kursus ini) menulis fungsi untuk menambahkan kolom ke pandas DataFrame. Sayangnya, ia menggunakan variabel yang dapat diubah sebagai nilai argumen default! Tunjukkan cara yang lebih baik agar mereka tidak mendapatkan perilaku yang tidak terduga.

def add_column(values, df=pandas.DataFrame()):
  """Tambahkan satu kolom `values` ke DataFrame `df`.
  Kolom akan diberi nama "col_<n>" di mana "n" adalah
  indeks numerik kolom tersebut.

  Args:
    values (iterable): Nilai untuk kolom baru
    df (DataFrame, optional): DataFrame yang akan diperbarui.
      Jika tidak ada DataFrame yang diberikan, satu akan dibuat secara default.

  Returns:
    DataFrame
  """
  df['col_{}'.format(len(df.columns))] = values
  return df

Latihan ini adalah bagian dari kursus

Menulis Function di Python

Petunjuk latihan

Ubah nilai default df menjadi nilai yang tidak dapat diubah (immutable) untuk mengikuti praktik terbaik.
Perbarui kode fungsi sehingga DataFrame baru dibuat jika pemanggil tidak memberikannya.

Latihan interaktif praktis

Cobalah latihan ini dengan menyelesaikan kode contoh berikut.

# Use an immutable variable for the default argument
def better_add_column(values, df=____):
  """Add a column of `values` to a DataFrame `df`.
  The column will be named "col_" where "n" is
  the numerical index of the column.

  Args:
    values (iterable): The values of the new column
    df (DataFrame, optional): The DataFrame to update.
      If no DataFrame is passed, one is created by default.

  Returns:
    DataFrame
  """
  # Update the function to create a default DataFrame
  if ____ is ____:
    df = pandas.DataFrame()
  df['col_{}'.format(len(df.columns))] = values
  return df

Edit dan Jalankan Kode

Latihan ini adalah bagian dari kursus

Menulis Function di Python

SkillTag.level.intermediateSkillTag.label

4.8+

Mulai Kursus Gratis

The goal of this course is to transform you into a Python expert, and so the first chapter starts off with best practices when writing functions. You'll cover docstrings and why they matter and how to know when you need to turn a chunk of code into a function. You will also learn the details of how Python passes arguments to functions, as well as some common gotchas that can cause debugging headaches when calling functions.

Exercise 1: Docstring Exercise 2: Menyusun sebuah docstring Exercise 3: Mengambil docstring Exercise 4: Docstring jadi penyelamat!Exercise 5: DRY dan "Lakukan Satu Hal"Exercise 6: Ekstrak sebuah fungsi Exercise 7: Membagi sebuah fungsi Exercise 8: Pass by assignment Exercise 9: Mutable atau immutable?Exercise 10: Praktik terbaik untuk argumen default

Latihan Saat Ini

If you've ever seen the "with" keyword in Python and wondered what its deal was, then this is the chapter for you! Context managers are a convenient way to provide connections in Python and guarantee that those connections get cleaned up when you are done using them. This chapter will show you how to use context managers, as well as how to write your own.

Exercise 1: Using context managers Exercise 2: The number of cats Exercise 3: The speed of cats Exercise 4: Writing context managers Exercise 5: The timer() context manager Exercise 6: A read-only open() context manager Exercise 7: Advanced topics Exercise 8: Context manager use cases Exercise 9: Scraping the NASDAQ Exercise 10: Changing the working directory

Decorators are an extremely powerful concept in Python. They allow you to modify the behavior of a function without changing the code of the function itself. This chapter will lay the foundational concepts needed to thoroughly understand decorators (functions as objects, scope, and closures), and give you a good introduction into how decorators are used and defined. This deep dive into Python internals will set you up to be a superstar Pythonista.

Exercise 1: Functions are objects Exercise 2: Building a command line data app Exercise 3: Reviewing your co-worker's code Exercise 4: Returning functions for a math game Exercise 5: Scope Exercise 6: Understanding scope Exercise 7: Modifying variables outside local scope Exercise 8: Closures Exercise 9: Checking for closure Exercise 10: Closures keep your values safe Exercise 11: Decorators Exercise 12: Using decorator syntax Exercise 13: Defining a decorator

Now that you understand how decorators work under the hood, this chapter gives you a bunch of real-world examples of when and how you would write decorators in your own code. You will also learn advanced decorator concepts like how to preserve the metadata of your decorated functions and how to write decorators that take arguments.

Exercise 1: Real-world examples Exercise 2: Print the return type Exercise 3: Counter Exercise 4: Decorators and metadata Exercise 5: Preserving docstrings when decorating functions Exercise 6: Measuring decorator overhead Exercise 7: Decorators that take arguments Exercise 8: Run_n_times()Exercise 9: HTML Generator Exercise 10: Timeout(): a real world example Exercise 11: Tag your functions Exercise 12: Check the return type Exercise 13: Great job!