How can I determine which arguments a Python function takes?

Question

Running the following code:

pdf = pdftotext.PDF(f,layout='raw')

produced this error:

'layout' is an invalid keyword argument for this function

Is there a way to list which arguments this, and any, function would take?

Answer 1

Use the help built-in function of python.

help([object])

Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.

Let's say you are coming from Python 2.7 and need help with the print function of Python 3. Go to the interactive prompt and type help(print):

>>> help(print)

   Help on built-in function print in module builtins:

   print(...)
       print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
   
       Prints the values to a stream, or to sys.stdout by default.
       Optional keyword arguments:
       file:  a file-like object (stream); defaults to the current sys.stdout.
       sep:   string inserted between values, default a space.
       end:   string appended after the last value, default a newline.
       flush: whether to forcibly flush the stream.
   (END)

As you can see print takes 4 keyword arguments (sep, end, file, flush). Press q when you are done to exit.

Answer 2

help(f) shows documentation and parameters for a python construct f, like a class or function.

Eg on the console

help(print)

shows

Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    end:   string appended after the last value, default a newline.
    flush: whether to forcibly flush the stream.

Help on my new function f ...

def f(): None

shows

Help on function f in module main:

f()

https://docs.python.org/3/library/functions.html#help

Answer 3

help function in python can be used to view the documentation for a class or a function. I like to keep an IPython interpreter running when coding in python. IPython provides operators like ? and ?? specifically for this purpose.