Reads an PWInput object from a string.

        Args:
            string (str): PWInput string

        Returns:
            PWInput object

def from_string(string):
        """
        Reads an PWInput object from a string.

        Args:
            string (str): PWInput string

        Returns:
            PWInput object
        """
        lines = list(clean_lines(string.splitlines()))

        def input_mode(line):
            if line[0] == "&":
                return ("sections", line[1:].lower())
            elif "ATOMIC_SPECIES" in line:
                return ("pseudo", )
            elif "K_POINTS" in line:
                return ("kpoints", line.split("{")[1][:-1])
            elif "CELL_PARAMETERS" in line or "ATOMIC_POSITIONS" in line:
                return ("structure", line.split("{")[1][:-1])
            elif line == "/":
                return None
            else:
                return mode

        sections = {"control": {}, "system": {}, "electrons": {}, 
                    "ions": {}, "cell":{}}
        pseudo = {}
        pseudo_index = 0
        lattice = []
        species = []
        coords = []
        structure = None
        site_properties = {"pseudo":[]}
        mode = None
        for line in lines:
            mode = input_mode(line)
            if mode == None:
                pass
            elif mode[0] == "sections":
                section = mode[1]
                m = re.match(r'(\w+)\(?(\d*?)\)?\s*=\s*(.*)', line)
                if m:
                    key = m.group(1).strip()
                    key_ = m.group(2).strip()
                    val = m.group(3).strip()
                    if key_ != "":
                        if sections[section].get(key, None) == None:
                            val_ = [0.0]*20 # MAX NTYP DEFINITION
                            val_[int(key_)-1] = PWInput.proc_val(key, val)
                            sections[section][key] = val_

                            site_properties[key] = []
                        else:
                            sections[section][key][int(key_)-1] = PWInput.proc_val(key, val) 
                    else:
                        sections[section][key] = PWInput.proc_val(key, val)

            elif mode[0] == "pseudo":
                m = re.match(r'(\w+)\s+(\d*.\d*)\s+(.*)', line)
                if m:
                    pseudo[m.group(1).strip()] = {}
                    pseudo[m.group(1).strip()]["index"] = pseudo_index
                    pseudo[m.group(1).strip()]["pseudopot"] = m.group(3).strip()
                    pseudo_index += 1
            elif mode[0] == "kpoints":
                m = re.match(r'(\d+)\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+)', line)
                if m:
                    kpoints_grid = (int(m.group(1)), int(m.group(2)), int(m.group(3)))
                    kpoints_shift = (int(m.group(4)), int(m.group(5)), int(m.group(6)))
                else:
                    kpoints_mode = mode[1]
            elif mode[0] == "structure":
                m_l = re.match(r'(-?\d+\.?\d*)\s+(-?\d+\.?\d*)\s+(-?\d+\.?\d*)', line)
                m_p = re.match(r'(\w+)\s+(-?\d+\.\d*)\s+(-?\d+\.?\d*)\s+(-?\d+\.?\d*)', line)
                if m_l:
                    lattice += [ float(m_l.group(1)), float(m_l.group(2)), float(m_l.group(3)) ]
                elif m_p:
                    site_properties["pseudo"].append(pseudo[m_p.group(1)]["pseudopot"])
                    species += [pseudo[m_p.group(1)]["pseudopot"].split(".")[0]]
                    coords += [[float(m_p.group(2)), float(m_p.group(3)), float(m_p.group(4))]]

                    for k, v in site_properties.items():
                        if k != "pseudo":
                            site_properties[k].append(sections['system'][k][pseudo[m_p.group(1)]["index"]])
                if mode[1] == "angstrom":
                    coords_are_cartesian = True
                elif mode[1] == "crystal":
                    coords_are_cartesian = False

        structure = Structure(Lattice(lattice), species, coords, 
                              coords_are_cartesian=coords_are_cartesian,
                              site_properties=site_properties)
        return PWInput(structure=structure, control=sections["control"],
                       system=sections["system"], electrons=sections["electrons"], 
                       ions=sections["ions"], cell=sections["cell"], kpoints_mode=kpoints_mode,
                       kpoints_grid=kpoints_grid, kpoints_shift=kpoints_shift)