Use Python str Variables in MATLAB

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This example shows how to use Python® str variables in MATLAB®.

Call Python Function with str Input Arguments

To call a Python function that takes a str input argument, pass a MATLAB string or a character vector. MATLAB automatically converts the values to the Python str type.

For example, the Python os.listdir function gets information about the contents of a folder, specified as type str. Create a character vector representing a valid folder and call os.listdir. The number of example folders is based on your installed product.

folder = fullfile(matlabroot,'help','examples');
F = py.os.listdir(folder);
exFolders = py.len(F)
exFolders = 
  Python int with properties:

    denominator: [1×1 py.int]
           imag: [1×1 py.int]
      numerator: [1×1 py.int]
           real: [1×1 py.int]

    3

Use Python str Type in MATLAB

In MATLAB, a Python string is a py.str variable. To use this variable in MATLAB, call char. For example, the Python os.path.pathsep function returns the Python path separator character, a semicolon (;). 

p = py.os.path.pathsep
p = 
  Python str with no properties.

    ;

To insert this character between path names, type:

['mypath' char(p) 'nextpath']
ans = 
'mypath;nextpath'

Read Elements in Python String

You can index into a Python string the same way you index into a MATLAB string. Create a MATLAB character vector and display a range of characters.

str = 'myfile';
str(2:end)
ans = 
'yfile'

Convert the character vector to a Python str type and display the same characters.

pstr = py.str(str);
pstr(2:end)
ans = 
  Python str with no properties.

    yfile

Pass MATLAB Backslash Control Character

To pass the backslash control character (\) as a Python str type, insert the new line control character \n by calling the MATLAB sprintf function. Python replaces \n with a new line.

py.str(sprintf('The rain\nin Spain.'))
ans = 
  Python str with no properties.

    The rain
    in Spain.

Without the sprintf function, both MATLAB and Python interpret \ as a literal backslash.

py.str('The rain\nin Spain.')
ans = 
  Python str with no properties.

    The rain\nin Spain.

Pass this string to the Python string method split. Python treats the MATLAB character vector as a raw string and adds a \ character to preserve the original backslash.

split(py.str('The rain\nin Spain.'))
ans = 
  Python list with values:

    ['The', 'rain\\nin', 'Spain.']

    Use string, double or cell function to convert to a MATLAB array.