写一个方法，把字符串转为数字，比如 str=”1234″，变成 int 1234。并且测试这个程序。

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<pre><code class=""language-python"" lang=""python"">def StrToInt(a):
res ,mult,flag = 0,1,1
if not isinstance(a,str):
raise TypeError(""a is not str"")
if a[0] =='-' or a[0] == '+':
if a[0] == '-':
flag = -1
a = a[1:]
for i in range(len(a)-1,-1,-1):
if '9' =a[i] = '0':
res +=(ord(a[i]) -48) * mult
mult = mult *10
else :
return 0
return res * flag

def test_strToInt2(self):
with pytest.raises(TypeError):
StrToInt(34)
</code></pre>

<pre><code class=""language-python"" lang=""python"">测试用例：
def test_strToInt3(self):
assert StrToInt('测试赛') == 0

def test_strToInt4(self):
assert StrToInt('+2147689') == 2147689

def test_strToInt5(self):
assert StrToInt('45') == 45

def test_strToInt6(self):
assert StrToInt('1a33') == 0

def test_strToInt7(self):
assert StrToInt('-5') == -5
</code></pre>

<pre><code> "“`