Repository: spyder-ide/spyder

Issue:
Error when copying and pasting into SimpleImputer.fit_transform()
## Description

### What steps will reproduce the problem?

<!--- You can use Markdown here --->

as soon as I paste "X[:,1:3]" in fit_transform parentheses, Issue Reporter always pops up:
```
imputer = SimpleImputer(missing_values=np.nan, strategy='mean')
X[:,1:3] = imputer.fit_transform(X[:,1:3])
```

However I have no noticeable problems. So the error message is the only problem.

### Traceback
```python-traceback
Traceback (most recent call last):
  File "D:\Programs\anaconda3\lib\site-packages\spyder\plugins\editor\extensions\snippets.py", line 52, in wrapper
    return f(self, *args, **kwargs)
  File "D:\Programs\anaconda3\lib\site-packages\spyder\plugins\editor\extensions\snippets.py", line 241, in _process_text
    self.insert_text(text, line, column)
  File "D:\Programs\anaconda3\lib\site-packages\spyder\plugins\editor\extensions\snippets.py", line 375, in insert_text
    snippet.placeholder = new_text_node
AttributeError: 'NoneType' object has no attribute 'placeholder'
```

## Versions

* Spyder version: 5.0.5 
* Python version: 3.8.8
* Qt version: 5.9.7
* PyQt5 version: 5.9.2
* Operating System: Windows 10

### Dependencies

```

# Mandatory:
atomicwrites >=1.2.0          :  1.4.0 (OK)
chardet >=2.0.0               :  4.0.0 (OK)
cloudpickle >=0.5.0           :  1.6.0 (OK)
cookiecutter >=1.6.0          :  1.7.2 (OK)
diff_match_patch >=20181111   :  20200713 (OK)
intervaltree >=3.0.2          :  3.1.0 (OK)
IPython >=7.6.0               :  7.22.0 (OK)
jedi =0.17.2                  :  0.17.2 (OK)
jsonschema >=3.2.0            :  3.2.0 (OK)
keyring >=17.0.0              :  23.0.1 (OK)
nbconvert >=4.0               :  6.1.0 (OK)
numpydoc >=0.6.0              :  1.1.0 (OK)
paramiko >=2.4.0              :  2.7.2 (OK)
parso =0.7.0                  :  0.7.0 (OK)
pexpect >=4.4.0               :  4.8.0 (OK)
pickleshare >=0.4             :  0.7.5 (OK)
psutil >=5.3                  :  5.8.0 (OK)
pygments >=2.0                :  2.9.0 (OK)
pylint >=1.0                  :  2.9.5 (OK)
pyls >=0.36.2;<1.0.0          :  0.36.2 (OK)
pyls_black >=0.4.6            :  0.4.6 (OK)
pyls_spyder >=0.3.2;<0.4.0    :  0.3.2 (OK)
qdarkstyle =3.0.2             :  3.0.2 (OK)
qstylizer >=0.1.10            :  0.1.10 (OK)
qtawesome >=1.0.2             :  1.0.2 (OK)
qtconsole >=5.1.0             :  5.1.0 (OK)
qtpy >=1.5.0                  :  1.9.0 (OK)
rtree >=0.9.7                 :  0.9.7 (OK)
setuptools >=39.0.0           :  52.0.0.post20210125 (OK)
sphinx >=0.6.6                :  4.0.2 (OK)
spyder_kernels >=2.0.4;<2.1.0 :  2.0.5 (OK)
textdistance >=4.2.0          :  4.2.1 (OK)
three_merge >=0.1.1           :  0.1.1 (OK)
watchdog >=0.10.3             :  1.0.2 (OK)
zmq >=17                      :  20.0.0 (OK)

# Optional:
cython >=0.21                 :  0.29.24 (OK)
matplotlib >=2.0.0            :  3.3.4 (OK)
numpy >=1.7                   :  1.20.3 (OK)
pandas >=1.1.1                :  1.3.0 (OK)
scipy >=0.17.0                :  1.6.2 (OK)
sympy >=0.7.3                 :  1.8 (OK)
```



Discussion:
Hey @AaronBiddle, thanks for reporting. We'll fix this issue in our next version (5.1.0), to be released shortly.

Resolving patch:
diff --git a/spyder/plugins/editor/extensions/snippets.py b/spyder/plugins/editor/extensions/snippets.py
--- a/spyder/plugins/editor/extensions/snippets.py
+++ b/spyder/plugins/editor/extensions/snippets.py
@@ -363,7 +363,7 @@ def insert_text(self, text, line, column):
             self._remove_selection(start, end)
             line, column = start
         node, snippet, text_node = self._find_node_by_position(line, column)
-        if node is None or text_node is None:
+        if node is None or snippet is None or text_node is None:
             self.reset()
             return
         tokens = tokenize(text)


Test patch: