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from string import Template

s = Template("there are ${howmany} ${lang} Quotation symbols")

print s.substitute(lang='Python',howmany=3)

>>>there are 3  Python Quotation symbols

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from string import Template

s = Template("there are $howmany $lang Quotation symbols")

print s.substitute(lang='Python',howmany=3)

>>>there are 3  Python Quotation symbols

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from string import Template

s = Template("there are ${ howmany } ${lang} Quotation symbols")

print s.substitute(lang='Python',howmany=3)

>>>Traceback (most recent call last):

  File "E:/�������/201703/DeepLearning/neural-networks-and-deep-learning-master/src/validation.py", line 39, in <module>

    print s.substitute(lang='Python',howmany=3)

  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 176, in substitute

    return self.pattern.sub(convert, self.template)

  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 173, in convert

    self._invalid(mo)

  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 146, in _invalid

    (lineno, colno))

ValueError: Invalid placeholder in string: line 1, col 11

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from string import Template

s = Template("there are ${ howmany } ${lang} Quotation symbols")

print s.substitute(lang='Python')

>>>Traceback (most recent call last):

  File "E:/�������/201703/DeepLearning/neural-networks-and-deep-learning-master/src/validation.py", line 39, in <module>

    print s.substitute(lang='Python')

  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 176, in substitute

    return self.pattern.sub(convert, self.template)

  File "C:\Users\wangxin\Anaconda2\lib\string.py", line 166, in convert

    val = mapping[named]

KeyError: 'howmany'

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from string import Template

s = Template("there are ${howmany} ${lang} Quotation symbols")

print s.safe_substitute(lang='Python')

>>>there are ${howmany} Python Quotation symbols