class_docstr: Represents Fourier sine/cosine series.
  
  Explanation
  ===========
  
  This class only represents a fourier series.
  No computation is performed.
  
  For how to compute Fourier series, see the :func:`fourier_series`
  docstring.
  
  See Also
  ========
  
  sympy.series.fourier.fourier_series
class_docstr_tok: ["Represents","Fourier","sine\/cosine","series",".","Explanation","===========","This","class","only","represents","a","fourier","series",".","No","computation","is","performed",".","For","how","to","compute","Fourier","series",",","see","the",":","func",":","`","fourier_series","`","docstring",".","See","Also","========","sympy.series.fourier.fourier_series"]
docstr: Return the first n nonzero terms of the series.
  
  If ``n`` is None return an iterator.
  
  Parameters
  ==========
  
  n : int or None
      Amount of non-zero terms in approximation or None.
  
  Returns
  =======
  
  Expr or iterator :
      Approximation of function expanded into Fourier series.
  
  Examples
  ========
  
  >>> from sympy import fourier_series, pi
  >>> from sympy.abc import x
  >>> s = fourier_series(x, (x, -pi, pi))
  >>> s.truncate(4)
  2*sin(x) - sin(2*x) + 2*sin(3*x)/3 - sin(4*x)/2
  
  See Also
  ========
  
  sympy.series.fourier.FourierSeries.sigma_approximation
code: def truncate(self, n=3):
      """
      Return the first n nonzero terms of the series.
  
      If ``n`` is None return an iterator.
  
      Parameters
      ==========
  
      n : int or None
          Amount of non-zero terms in approximation or None.
  
      Returns
      =======
  
      Expr or iterator :
          Approximation of function expanded into Fourier series.
  
      Examples
      ========
  
      >>> from sympy import fourier_series, pi
      >>> from sympy.abc import x
      >>> s = fourier_series(x, (x, -pi, pi))
      >>> s.truncate(4)
      2*sin(x) - sin(2*x) + 2*sin(3*x)/3 - sin(4*x)/2
  
      See Also
      ========
  
      sympy.series.fourier.FourierSeries.sigma_approximation
      """
      if n is None:
          return iter(self)
  
      terms = []
      for t in self:
          if len(terms) == n:
              break
          if t is not S.Zero:
              terms.append(t)
  
      return Add(*terms)
  
imports: from sympy.core.numbers import oo, pi
  from sympy.core.symbol import Wild
  from sympy.core.expr import Expr
  from sympy.core.add import Add
  from sympy.core.containers import Tuple
  from sympy.core.singleton import S
  from sympy.core.symbol import Dummy, Symbol
  from sympy.core.sympify import sympify
  from sympy.functions.elementary.trigonometric import sin, cos, sinc
  from sympy.series.series_class import SeriesBase
  from sympy.series.sequences import SeqFormula
  from sympy.sets.sets import Interval
  from sympy.utilities.iterables import is_sequence
label_desc: Use image node_id 14 for calling the FourierSeries obj's underlying member method code with example usage: obj.truncate(n) and returns: Add, iter